Sunday, June 29, 2008
GOING TO GEORGE MASON UNIVERSITY.......
GUYS ME MOST PROBABLY WILL BE GOING TO GEORGE MASON UNIVERSITY FOR MS IN BIOINORMATICS AND COMPUTATIONAL BIOLOGY....HEARD ABT IT THEM TELL ME ABT IT SITE IS www.gmu.edu and www.binf.gmu.edu mail me at rons.shah@gmail.com
Results of my project
Figure 3.6: Polyacralamide gel depicting the protein pattern on different medium (Bands from left to right). 1. Molecular marker. 2, 3. Fungus in Potato Dextrose Broth (PDB). 3, 4. Fungus in Chitin. 4, 5. Fungus in Starch(copyright@ronakshah)
.png)
Figure 3.5: HPLC profile of extract of Fusarium moniliforme grown on different medium(copyright@ronakshah)
.png)
Figure 3.4: Protein estimation graph of Fusarium moniliforme with reference to protein concentration vs. absorbance (630nm) [Red line is the Standard Protein and black line is the estimated protein](copyright@ronakshah)
.png)
.png)
Figure 3.1: a. Growth of F.moniliforme at Room Temperature. b. Growth of F.moniliforme at 25○C. c. Growth of F.moniliforme at 300○C. d. Growth of F.moniliforme at 40 ○C.(Copyright@RONAKSHAH)
Figure 3.2: Growth of Fusarium moniliforme at different pH (COPYRIGHT@RONAKSHAH)
Visa Process
1)Advise from me For visa matter
2)Go to nearest HDFC Bank with zerox of your passport and pay around Rs five thousand five hundred approximately. Not all HDFC does take US student visa fees, you have to check
3)Collect student visa fees receipt. Keep the receipts three original copies that you get at safe place ( Most Important) . Make it point it has bar code on that.
4)Take out 04 photographs of 50mmX 50mm with white background.
5)After three working days after HDFC receipt you can log on to www.vfs-usa.co.in to fill the non immigration visa form. However you can see the available nonimmigrant visa dates without HDFC receipt but cannot fill the form.
6)To take the date you need at least one admit (I-20) in hand. You can take the date on any available I-20. However you can change I-20 of other college 10 days prior visa interview. However you can change the college before visa interview.
7)You can also reschedule the visa interview date at any point of time only thing is that it should be latest 10 days ahead of your earlier visa date.
8)Five working days prior to visa interview you have to submit following documents at VFS US VISA center ground floor, tirupati apartment diagonal opposite to Mahalaxmi temple, near Nalli show room
a)Copy of Visa Form online you filled with photo. Form number DS156 has two pages which you have to print back to back ., 157 you can print seperatelyb)Zerox of I-20c)Zerox of Passportd)Sevis Fee Receipt ( not mandatory but mandatory during visa intere)view)f)HDFC Receipt g)On line appointment proof you got while taking date online
7) Sevis Fee Receipt you can get online printed by logging to fmjfee.com using credit card for 100 USD. But Sevis fees is to paid only when you finalize the university of your choice. Sevis fee is mandatory as per USA immigration law to be paid by the student.
2)Go to nearest HDFC Bank with zerox of your passport and pay around Rs five thousand five hundred approximately. Not all HDFC does take US student visa fees, you have to check
3)Collect student visa fees receipt. Keep the receipts three original copies that you get at safe place ( Most Important) . Make it point it has bar code on that.
4)Take out 04 photographs of 50mmX 50mm with white background.
5)After three working days after HDFC receipt you can log on to www.vfs-usa.co.in to fill the non immigration visa form. However you can see the available nonimmigrant visa dates without HDFC receipt but cannot fill the form.
6)To take the date you need at least one admit (I-20) in hand. You can take the date on any available I-20. However you can change I-20 of other college 10 days prior visa interview. However you can change the college before visa interview.
7)You can also reschedule the visa interview date at any point of time only thing is that it should be latest 10 days ahead of your earlier visa date.
8)Five working days prior to visa interview you have to submit following documents at VFS US VISA center ground floor, tirupati apartment diagonal opposite to Mahalaxmi temple, near Nalli show room
a)Copy of Visa Form online you filled with photo. Form number DS156 has two pages which you have to print back to back ., 157 you can print seperatelyb)Zerox of I-20c)Zerox of Passportd)Sevis Fee Receipt ( not mandatory but mandatory during visa intere)view)f)HDFC Receipt g)On line appointment proof you got while taking date online
7) Sevis Fee Receipt you can get online printed by logging to fmjfee.com using credit card for 100 USD. But Sevis fees is to paid only when you finalize the university of your choice. Sevis fee is mandatory as per USA immigration law to be paid by the student.
Saturday, June 7, 2008
Hey guys now lately i am busy with my pro working on fusarium spp
Characterization of Entemopathogenic Fungus Fusarium Moniliforme
1. Introduction
The really basic division among life forms is between the simpler Prokaryotes and the more complex Eukaryotes. Look at the diagram below: it shows the way in which we think the Kingdoms evolved. It is based on molecular evidence: base sequences from ribosomal RNA.
Figure 1:Evolution of Kingdoms
The earliest forms of life, which appeared about 3,500 - 3,800 million years ago, were prokaryotes. We tend to define them by their relative morphological simplicity, and by the absence of many features found in more modern cells. Although their modern descendants have a single chromosome, this is not found inside a nucleus, and their cytoplasm contains no mitochondria or plastids (cytoplasmic organelles). These organisms make up the baseline Kingdoms Archaebacteria and Eubacteria (These are sometimes called Domains, and regarded as having equal 'rank' with the whole of the Eukaryota). It is also now believed that the earliest cells swapped genes in lateral transfers before the three domains became distinct. Most gene-swapping now takes place within, rather than among, domains, which is one reason they are still recognizable entities.
The prokaryotes had the world to themselves for 1,500 million years (they did, however, invent photosynthesis during that time). Not until about 2 billion years ago did life take the next giant step, the evolution of the eukaryotic cell. Many, perhaps most, biologists now believe that this arose as a result of the mutually beneficial symbiotic union of several different kinds of prokaryote within another host prokaryote. At least two kinds of modern organelle have been found to retain some of their original independent DNA: (1) Mitochondria, which specialize in the oxidation of 3-carbon organic acids (the Krebs cycle), providing an immediately available energy supply in the form of ATP; and (2) Plastids, which may contain photosynthetic pigments and enzymes (chloroplasts), or may store food. Some biologists also think that flagella were once free-living prokaryotes.
Eukaryotic cells also have their DNA organized into a number of discrete chromosomes, which are found inside a membrane-bounded nucleus. Cell division in eukaryotes involves a complex process called mitosis. The nuclear membrane breaks down, a mitotic spindle of microtubules develops, and the chromosomes are duplicated. Then the daughter chromosomes separate and are pulled to opposite poles by the contracting spindle fibres. Each set of chromosomes then becomes enclosed by a new nuclear membrane, and the cell finally divides into two.
Prokaryotic cells have only a single, usually circular chromosome, and do not undergo mitosis. They usually divide by a much simpler process called binary fission. Mitosis, with its very accurate duplication and sharing of the genetic material, seems to have been a crucial invention. Only eukaryotic cells, with their precisely regulated genetic mechanisms, apparently had the potential to evolve into more complex, multicellular organisms in which cells are organized into different tissues and organs. All prokaryotes are still microbes.
Now look at the Kingdom diagram again (above). The Archaebacteria and the Eubacteria are prokaryotes. The eukaryotes encompass the other five Kingdoms, and it is in these other Kingdoms that the dazzling evolutionary explosion of new taxa has occurred. The diagram shows five eukaryote Kingdoms: Protista (now often called Protozoa), Chromista, Plantae, Animalia and Eumycota.
The burst of eukaryote evolution was made possible by, among other things, a modified form of mitosis called meiosis or reduction division. In many organisms this produces special sex cells called gametes. Each of these cells has a single set of chromosomes (we say that the cells are haploid). When two gametes from compatible parent organisms fuse, the resulting cell (the zygote) has two sets of chromosomes (we call this condition diploid). In plants and animals, zygotes develop into diploid, multicellular organisms, but in most fungi the vegetative phase is always haploid, so meiosis must take place in the zygote. Whether meiosis happens in the zygote, or at the other end of the life cycle, during the formation of gametes, it is responsible for the reassortment of the genetic information built into the chromosomes. New features are constantly being added to the pool of genetic material by the process of mutation, but sexual reproduction is the mechanism by which this pool is recombined each generation in most eukaryotic organisms, producing an endless supply of variation upon which the processes of natural selection can work. This is one of the key secrets of eukaryote diversity.
The radiation of the two largely unicellular Kingdoms (Protozoa and Chromista) shows how the evolution of the eukaryotic cell expanded life's horizons. But the full potential of the new teamwork -- we call it that, since several prokaryotes cooperate to make one functional eukaryotic cell -- was not realized until cells, as well as cell components, began to cooperate. When organisms became multicellular, different cells could assume different, specialised functions. This division of labour eventually led to the development of tissues and organs, and ultimately permitted the evolution of complex beings like ourselves, beings with almost infinitely expanded capabilities (both wonderful and terrible).
Three new multicellular Kingdoms arose, exemplifying three different ways of life. Multicellular organisms which could photosynthesize -- make their own food from simple inorganic precursors -- were eaten by other multicellular organisms that lacked this talent, and both were recycled after death by a third group. These groups we call producers, consumers and decomposers -- the plants, the animals and the fungi. We recognize about 9 phyla of plants, about 32 phyla of animals, and 6 phyla of fungi (2 chromistan and 4 eumycotan).
The world being what it is, the picture is not as simple as we might like. Some of the divergent paths of evolution have come together again, almost as they did at the birth of the eukaryotes, and many organisms that seem unitary are in fact partnerships or even consortia. Lichens, for example, always incorporate both an alga (eukaryotic or prokaryotic) and a fungus.
1.1 Five Kingdom Classification System
Once upon a time, all living things were lumped together into two kingdoms, namely plants and animals (at least, that's how I learned it). Animals included every living thing that moved, ate, and grew to a certain size and stopped growing. Plants included every living thing that did not move or eat and that continued to grow throughout life. It became very difficult to group some living things into one or the other, so early in the past century the two kingdoms were expanded into five kingdoms: Protista (the single-celled eukaryotes); Fungi (fungus and related organisms); Plantae (the plants); Animalia (the animals); Monera (the prokaryotes). Many biologists now recognize six distinct kingdoms, dividing Monera into the Eubacteria and Archeobacteria.
All I can say is that the sytem holds true for this week, at least. It might even hold up for a century or two. Accepted systems of classification have changed at a far faster pace than the species have taken to evolve, that's for certain.
Kingdoms are divided into categories called phyla, each phylum is divided into classes, each class into orders, each order into families, each family into genera, and each genus into species. A species represents one type of organism, such as dog, tiger shark, Ameoba proteus (the common amoeba), Homo sapiens (us), or Acer palmatum (Japanese maple). Note that species names should be underlined or written in italics.
Classifying larger organisms into kingdoms is usually easy, but in a microenvironment it can be tricky. If you have had a little biology, a good exercise is to describe individual living things, and to try to classify them as to kingdom.
1.1.1 Kingdom Monera (includes Eubacteria and Archeobacteria)
Individuals are single-celled, may or may not move, have a cell wall, have no chloroplasts or other organelles, and have no nucleus. Monera are usually very tiny, although one type, namely the blue-green bacteria, look like algae. They are filamentous and quite long, green, but have no visible structure inside the cells. No visible feeding mechanism. They absorb nutrients through the cell wall or produce their own by photosynthesis.
1.1.2 Kingdom Protista
Protists are single-celled and usually move by cilia, flagella, or by amoeboid mechanisms. There is usually no cell wall, although some forms may have a cell wall. They have organelles including a nucleus and may have chloroplasts, so some will be green and others won't be. They are small, although many are big enough to be recognized in a dissecting microscope or even with a magnifying glass. Nutrients are acquired by photosynthesis, ingestion of other organisms, or both.
1.1.3 Kingdom Fungi
Fungi are multicellular,with a cell wall, organelles including a nucleus, but no chloroplasts. They have no mechanisms for locomotion. Fungi range in size from microscopic to very large ( such as mushrooms). Nutrients are acquired by absorption. For the most part, fungi acquire nutrients from decaying material.
1.1.4 Kingdom Plantae
Plants are multicellular and most don't move, although gametes of some plants move using cilia or flagella. Organelles including nucleus, chloroplasts are present, and cell walls are present. Nutrients are acquired by photosynthesis (they all require sunlight).
1.1.5 Kingdom Animalia
Animals are multicellular, and move with the aid of cilia, flagella, or muscular organs based on contractile proteins. They have organelles including a nucleus, but no chloroplasts or cell walls. Animals acquire nutrients by ingestion.
2. Kingdom Fungi
The organisms of the fungal lineage include mushrooms, rusts, smuts, puffballs, truffles, morels, molds, and yeasts, as well as many less well-known organisms. More than 70,000 species of fungi have been described; however, some estimates of total numbers suggest that 1.5 million species may exist.
As the sister group of animals and part of the eukaryotic crown group that radiated about a billion years ago, the fungi constitute an independent group equal in rank to that of plants and animals. They share with animals the ability to export hydrolytic enzymes that break down biopolymers, which can be absorbed for nutrition. Rather than requiring a stomach to accomplish digestion, fungi live in their own food supply and simply grow into new food as the local environment becomes nutrient depleted.
Most biologists have seen dense filamentous fungal colonies growing on rich nutrient agar plates, but in nature the filaments can be much longer and the colonies less dense. When one of the filaments contacts a food supply, the entire colony mobilizes and reallocates resources to exploit the new food. Should all food become depleted, sporulation is triggered. Although the fungal filaments and spores are microscopic, the colony can be very large with individuals of some species rivaling the mass of the largest animals or plants.
Figure 2: Hyphae of a wood-decaying fungus found growing on the underside of a fallen log. The metabolically active hyphae have secreted droplets on their surfaces. Copyright © M. Blackwell 1996.
Prior to mating in sexual reproduction, individual fungi communicate with other individuals chemically via pheromones. In every phylum at least one pheromone has been characterized, and they range from sesquiterpines and derivatives of the carotenoid pathway in chytridiomycetes and zygomycetes to oligopeptides in ascomycetes and basidiomycetes.
Within their varied natural habitats fungi usually are the primary decomposer organisms present. Many species are free-living saprobes (users of carbon fixed by other organisms) in woody substrates, soils, leaf litter, dead animals, and animal exudates. The large cavities eaten out of living trees by wood-decaying fungi provide nest holes for a variety of animals, and extinction of the ivory billed woodpecker was due in large part to loss, through human activity, of nesting trees in bottom land hardwoods. In some low nitrogen environments several independent groups of fungi have adaptations such as nooses and sticky knobs with which to trap and degrade nematodes and other small animals. A number of references on fungal ecology are available.
However, many other fungi are biotrophs, and in this role a number of successful groups form symbiotic associations with plants (including algae), animals (especially arthropods), and prokaryotes. Examples are lichens, mycorrhizae, and leaf and stem endophytes. Although lichens may seem infrequent in polluted cities, they can form the dominant vegetation in nordic environments, and there is a better than 80% chance that any plant you find is mycorrhizal. Leaf and stem endophytes are a more recent discovery, and some of these fungi can protect the plants they inhabit from herbivory and even influence flowering and other aspects of plant reproductive biology. Fungi are our most important plant pathogens, and include rusts, smuts, and many ascomycetes such as the agents of Dutch elm disease and chestnut blight. Among the other well known associations are fungal parasites of animals. Humans, for example, may succumb to diseases caused by Pneumocystis (a type of pneumonia that affects individuals with supressed immune systems), Coccidioides (valley fever), Ajellomyces (blastomycosis and histoplasmosis), and Cryptococcus (cryptococcosis).
Figure 3: The fluffy white hyphae of the mycorrhizal fungus Rhizopogon rubescens has enveloped the smaller roots of a Virginia pine seedling. Note that some of the mycelium extends out into the surrounding environment. Copyright © J. B. Anderson 1996.
Figure 4: Entomophthora, "destroyer of insects", is the agent of a fungual infection that kills flies. After their death the fungal growth erupts through the fly cuticle, and dispersal by forcible spore discharge is a source of inoculum for infection of new flies. Copyright © G. L. Barron 1996.
Fungal spores may be actively or passively released for dispersal by several effective methods. The air we breathe is filled with spores of species that are air dispersed. These usually are species that produce large numbers of spores, and examples include many species pathogenic on agricultural crops and trees. Other species are adapted for dispersal within or on the surfaces of animals (particularly arthropods). Some fungi are rain splash or flowing water dispersed. In a few cases the forcible release of spores is sufficient to serve as the dispersal method as well. The function of some spores is not primarily for dispersal, but to allow the organisms to survive as resistant cells during periods when the conditions of the environment are not conducive to growth.
Figure 5: Diversity of Spores among Fungi.
Fungi are vital for their ecosystem functions, some of which we have reviewed in the previous paragraphs. In addition a number of fungi are used in the processing and flavoring of foods (baker's and brewer's yeasts, Penicillia in cheese-making) and in production of antibiotics and organic acids. Other fungi produce secondary metabolites such as aflatoxins that may be potent toxins and carcinogens in food of birds, fish, humans, and other mammals.
A few species are studied as model organisms that can be used to gain knowledge of basic processes such as genetics, physiology, biochemistry, and molecular biology with results that are applicable to many organisms. Some of the fungi that have been intensively studied in this way include Saccharomyces cereviseae, Neurospora crassa, and Ustilago maydis.
Most phyla appear to be terrestrial in origin, although all major groups have invaded marine and freshwater habitats. An exception to this generality is the flagellum-bearing phyla Chytridiomycota, Blastocladiomycota, and Neocallimastigomycota (collectively referred to as chytrids), which probably had an aquatic origin. Extant chytrid species also occur in terrestrial environments as plant pathogenic fungi, soil fungi, and even as anaerobic inhabitants of the guts of herbivores such as cows (all Neocallimastigomycota).
2.1 Characteristics
Fungi are characterized by non-motile bodies (thalli) constructed of apically elongating walled filaments (hyphae), a life cycle with sexual and asexual reproduction, usually from a common thallus, haploid thalli resulting from zygotic meiosis, and heterotrophic nutrition. Spindle pole bodies, not centrioles, usually are associated with the nuclear envelope during cell division. The characteristic wall components are chitin (beta-1,4-linked homopolymers of N-acetylglucosamine in microcrystalline state) and glucans primarily alpha-glucans (alpha-1,3- and alpha-1,6- linkages).
Figure 6: Portion of a hypha of a zygomycete stained with a blue dye to show the many nuclei present. Many other fungi have septations that devide the hyphae into compartments that usually contain one to several nuclei per compartment. Copyright © M. Blackwell 1996.
Figure 7: Transmission electron micrograph showing duplicated spindle pole body of a prophase I meiotic nucleus of a basidiomycete Exobasidium. Only chytrids among fungi have centrioles and lack spindle pole bodies. Copyright © Beth Richardson 1996.
Exceptions to this characterization of fungi are well known, and include the following: Most species of chytrids have cells with a single, smooth, posteriorly inserted flagellum at some stage in the life cycle, and centrioles are associated with nuclear division. The life cycles of most chytrids are poorly studied, but some (Blastocladiomycota) are known to have zygotic meiosis (therefore, alternation between haploid and diploid generations). Certain members of Mucoromycotina, Ascomycota, and Basidiomycota may lack hyphal growth during part or all of their life cycles, and, instead, produce budding yeast cells. Most fungal species with yeast growth forms contain only minute amounts of chitin in the walls of the yeast cells. A few species of Ascomycota (Ophiostomataceae) have cellulose in their walls, and certain members of Blastocladiomycota and Entomophthoromycotina lack walls during part of their life cycle.
2.2 Fossil Record
Based on the available fossil record, fungi are presumed to have been present in Late Proterozoic (900-570 mya). Terrestrial forms of purported ascomycetes are reported in associations with microarthropods in the Silurian Period (438-408 mya). Fossil hyphae in association with wood decay and fossil chytrids and Glomales-Endogonales representatives associated with plants of the Rhynie Chert are reported from the Devonian Period (408-360 mya). Fungal fossil diversity increased throughout the Paleozoic Era with all modern classes reported in the Pennsylvanian Epoch (320-286 mya).
A first attempt to match molecular data on fungal phylogeny to the geological record shows general agreement, but does point out some conflicts between the two types of data.
2.4 Biogeography
Wherever adequate moisture, temperature, and organic substrates are available, fungi are present. Although we normally think of fungi as growing in warm, moist forests, many species occur in habitats that are cold, periodically arid, or otherwise seemingly inhospitable. It is important to recognize that optimum conditions for growth and reproduction vary widely with fungal species. Diversity of most groups of fungi tends to increase in tropical regions, but detailed studies are only in their infancy .
Although many saprobic and plant pathogenic species with low substrate specificity and effective dispersal systems have broad distributions, gene flow appears to be restricted in many fungi. For these species large bodies of water such as the Atlantic and Pacific Oceans create barriers to gene exchange. Some distributions are limited by substrate availability, and dramatic examples come from parasites of Gondowanan plants; one of these is the Southern Hemisphere distribution of the ascomycete Cyttaria, corresponding with part of the distribution of its host plant Nothofagus. The fossil record shows that fungi were present in Antarctica, as is the case for other organisms with Gondwanan distributions. Arthropod associates also may show distributions throughout part or all of a host range, and some fungal species (ex. wood wasp associates) occur outside the range of the associated arthropod.
2.5 Kingdom Fungi Classification
All living things can be classified into one of five fundamental Kingdoms of life, and the term fungus refers generically to all members of the Kingdom Fungi. There are more than a million species of fungi, but only about 400 cause diseases relevant to man, animals, or plants. The majority of the pathogenic species are classified within the Phyla Zygomycota, Basidiomycota, Ascomycota, or the form group Fungi Imperfecti. Fungi (the singular form is 'fungus'), including those pathogenic to humans and animals, are eukaryotic microorganisms.
Figure 8: Classification of Fungi.
2.5.1 Phylogeny Based Classification
Figure 9: Phylogeny modified from James et al., 2006a, 2006b; Liu et al., 2006; Seif et al., 2005; Steenkamp et al., 2006.
2.5.1.1 Basidomycota
The Basidiomycota contains about 30,000 described species, which is 37% of the described species of true Fungi. The most conspicuous and familiar Basidiomycota are those that produce mushrooms, which are sexual reproductive structures. The Basidiomycota also includes yeasts (single-celled forms; Fell et al. 2001) and asexual species. Basidiomycota are found in virtually all terrestrial ecosystems, as well as freshwater and marine habitats.
Basidiomycota have a huge impact on human affairs and ecosystem functioning. Many Basidiomycota obtain nutrition by decaying dead organic matter, including wood and leaf litter. Thus, Basidiomycota play a significant role in the carbon cycle. Unfortunately, Basidiomycota frequently attack the wood in buildings and other structures, which has negative economic consequences for humans.
Symbiotic lifestyles (intimate associations with other living organisms) are well developed in the Basidiomycota. Symbiotic Basidiomycota include important plant pathogens, such as "rusts" (Uredinales) and "smuts" (Ustilaginales), which attack wheat and other crops. Other symbiotic Basidiomycota cause diseases in animals, including humans. Not all symbiotic Basidiomycota cause obvious harm to their partners, however. For example, some Basidiomycota, as well as a handful of Ascomycota, form ectomycorrhizae, which are associations with the roots of vascular plants (principally forest trees such as oaks, pines, dipterocarps, and eucalypts. Ectomycorrhizal Basidiomycota help their plant partners obtain mineral nutrients from the soil, and in return they receive sugars that the plants produce through photosynthesis. Other symbiotic Basidiomycota form associations with insects, including leaf-cutter ants, termites, scale insects, woodwasps, and bark beetles.
Humans have found diverse uses for Basidiomycota. Mushrooms, both cultivated and wild, are eaten in many countries. For the untrained, mushroom-hunting is a risky endeavor, because some Basidiomycota produce deadly toxins. The basidiomycete toxin phalloidin (from the mushroom Amanita phalloides) binds actin, which is a component of microfilaments. Fluorescent stains that incorporate phalloidin are used by cell biologists to visualize the cytoskeleton. Other "toxins" produced by Basidiomycota include hallucinogens, which are produced by members of the genus Psilocybe (and other groups). Species of Psilocybe have traditionally been used in Central American indigenous cultures as a spiritual tool, and are now cultivated for the illicit drug trade. Other biochemical compounds of Basidiomycota that have practical uses include astaxanthin, a red pigment produced by the basidiomycetous yeast Phaffia (used to add color to farmed salmon), and certain enzymes from wood-decaying Basidiomycota that have potential applications in paper production and bioremediation (decontamination of polluted environments using biological agents).
Figure 10: SEM of the surface of a mushroom gill (Coprinus cinereus: Agaricomycotina) showing several basidia, some with four basidiospores attached.(From McLaughlin, et al. 1985; used with permission © McLaughlin, Beckett and Yoon 1985.)
2.5.1.2 Ascomycota
The Ascomycota, or sac fungi, is monophyletic and accounts for approximately 75% of all described fungi. It includes most of the fungi that combine with algae to form lichens, and the majority of fungi that lack morphological evidence of sexual reproduction. Among the Ascomycota are some famous fungi: Saccharomyces cerevisiae, the yeast of commerce and foundation of the baking and brewing industries (not to mention molecular developmental biology), Penicillium chrysogenum, producer of penicillin, Morchella esculentum, the edible morel, and Neurospora crassa, the "one-gene-one-enzyme" organism. There are also some infamous Ascomycota, a few of the worst being: Aspergillus flavus, producer of aflatoxin, the fungal contaminant of nuts and stored grain that is both a toxin and the most potent known natural carcinogen, Candida albicans, cause of thrush, diaper rash and vaginitis, and Cryphonectria parasitica, responsible for the demise of 4 billion chestnut trees in the eastern USA.Asexual Ascomycota, such as Penicillium or Candida species, used to be classified separately in the Deuteromycota because sexual characters were necessary for Ascomycota classification. However, the comparison of nucleic acid sequence, as well as nonsexual phenotypic characters, have permitted the integration of asexual fungi into the Ascomycota. The Deuteromycota is no longer recognized as a formal taxon in fungal systematics.
Figure 11: In hyphal Ascomycota, the youngest, terminal hyphal segments develop into 8-spored asci. Asci of a hyphal Ascomycota (Pezizomycotina), Podospora , © R. Vilgalys 1996. Ascus of a yeast (Saccharomycotina), Saccharomyces, © J. Taylor 1996.
2.5.1.3 Glomeromycota
Although the Glomeromycota comprise a group of fungi virtually unknown to the broad public, they are essential for terrestrial ecosystem function. Members of this group are mutualistic symbionts that form arbuscular mycorrhizal (AM) associations intracellularly within the roots of the vast majority of herbaceous plants and tropical trees. This type of symbiosis is termed mutualistic because the fungus and host plant both benefit from this intimate association. The fungal symbiont receives carbohydrates from the plant in exchange for functioning as an extended root system, thereby dramatically improving mineral uptake by the plant roots. Although there are various types of mycorrhizas, involving different fungal and plant symbionts, the arbuscular mycorrhiza type is the most widespread. The phylum Glomeromycota currently comprises approximately 150 described species distributed among ten genera, most of which are defined primarily by spore morphology. Recently, DNA sequences have also been used to circumscribe taxa.
Figure 12: Spores of Scutellospora castanea (isolate BEG1, photo © Annemarie Brennwald). Spore diameter approximately 220 µm.
2.5.1.4 Zygomycota
The Zygomycota contains approximately 1% of the described species of true Fungi (~900 described species; Kirk et al. 2001). The most familiar representatives include the fast-growing molds that we encounter on spoiled strawberries (Figure 1) and other fruits high in sugar content. Although these fungi are common in terrestrial and aquatic ecosystems, they are rarely noticed by humans because they are of microscopic size. Colonial growth and the taxonomically informative asexual reproductive structures Zygomycota produce are typically studied after culturing on various agar media. Direct microscopic observation of suitable substrates is required for those species that either have not or cannot be cultured. Fewer than half of the species have been cultured and the majority of these are members of the Mucorales, a group that includes some of the fastest growing fungi.
Click on an image to view larger version & data in a new window
Figure 13: Moldy strawberries covered with Rhizopus mycelium. Photo K. O'Donnell.
Zygomycota are defined and distinguished from all other fungi by sexual reproduction via zygospores following gametangial fusion (Figure 14A,B) and asexual reproduction by uni-to-multispored sporangia (Figure 15A,B) within which nonmotile, single-celled sporangiospores are produced. The phylum comprises at least seven phylogenetically diverse orders. Monophyly of the phylum and interrelationships among orders are currently under intensive investigation using multilocus DNA sequence data. This introduction to the Zygomycota does not include the order comprising the arbuscular mycorrhizal (AM) fungi, the Glomales, because it has been elevated to the rank of phylum, the Glomeromycota (Schüßler et al. 2001). One other group, the Microsporidia, were previously considered protozoa, however, DNA, biochemistry, and morphology suggest these highly reduced, obligate, intracellular parasites may have evolved from a zygomycete-like ancestor.
Click on an image to view larger version & data in a new window
Figure 14: Sexual reproduction. (A) Scanning electron micrograph of gametangial fusion in Mucor mucedo. (B) Highly ornamented zygosporangium of Mycotypha africana. (From O'Donnell 1979).
Figure 15: Asexual reproduction. (A) Scanning electron micrograph of unispored sporangia of Benjaminiella poitrasii and (B) dehisced multispored sporangium of Gilbertella persicaria releasing sporangiospores. (From O'Donnell 1979).
Zygomycota are arguably the most ecologically diverse group of fungi, functioning as saprophytes on substrates such as fruit, soil, and dung (Mucorales), as harmless inhabitants of arthropod guts (Harpellales), as plant mutualists forming ectomycorrhizae (Endogonales), and as pathogens of animals, plants, amoebae, and especially other fungi (all Dimargaritales and some Zoopagales are mycoparasites). A number of species are used in Asian food fermentations, such as Rhizopus oligosporus in the Indonesian staple tempeh, and Actinomucor elegans in Chinese cheese or sufu.
Conversely, some species have a negative economic impact on human affairs by causing storage rots of fruits (particularly strawberries by Rhizopus stolonifer [Figure 13]), as agents of plant disease (e.g., Choanephora cucurbitarum flower rot of curcurbits), while other species can cause life-threatening opportunistic infections of diabetic, immuno-suppressed, and immuno-compromised patients. In addition to some Mucorales that attack immuno-suppressed humans, several species of microsporidia cause serious human infections. Some zygomycetes are regularly isolated by veterinarians from domesticated animals in tropical and subtropical regions of the world, including the US gulf states.
2.5.1.5 Blastocladiomycota
The Blastocladiomycota were previously considered a taxonomic clade within the Chytridiomycota. Recent molecular data and ultrastructural characteristics, however, place the Blastocladiomycota as a sister clade to the Zygomycota, Glomeromycota, and Dikarya (Ascomycota and Basiomycota). The blastocladiomycetes are fungi that are saprotrophs and parasites of all eukaryotic groups and undergo sporic meiosis unlike their close relatives, the chytrids, which mostly exhibit zygotic meiosis.
Figure 16: Blastocladiella asperosperma
2.5.1.6 Chytridiomycota
The Phylum Chytridiomycota (chytrids) includes two classes, Chytridiomycetes and Monoblepharidomycetes, each of which is monophyletic based on molecular analyses. Because of their genetic and morphological divergence, two groups of zoosporic fungi once included among chytrids are now classified as separate Phyla, Blastocladiomycota and Neocallimastigomycota. The Chytridiomycetes are currently separated into five orders [Chytridiales , Rhizophydiales , Spizellomycetales, Rhizophlyctidales, and Lobulomycetales] . Molecular phylogenetic analyses have demonstrated that each of these orders is monophyletic, except for the current circumscription of the Chytridiales. Work is progressing on characterization of clades for groups formerly included in the Chytridiales. These groups, which do not cluster with recognized members of the Chytridiales, are listed here as provisional orders. Molecular analyses place two genera assigned to the Spizellomycetales outside of the core chytrid clade. The genus Rozella appears basal to the core chytrids and Olpidium brassicae radiates among zygomycetes. Thus, their classification is uncertain at this time (incertae sedis).
Figure 17: Catenochytridium sp.on Eriocaulon
2.5.1.7 Neocallimastigomycota
The Neocallimastigomycota were earlier placed in the phylum Chytridomycota. Members of this small phylum are anaerobic organisms, living in the digestive system of larger herbivorous mammals and possibly in other terrestrial and aquatic environments. They lack mitochondria but contain hydrogenosomes of mitochondrial origin. As the related chrytrids, neocallimastigomycetes form zoospores that are posteriorly uniflagellate or polyflagellate.
3. Importance of Fungi
3.1 Fungi are agents of biodegradation and biodeterioration
Saprotropic fungi utilise dead organic materials as sources of nutrients and are responsible for the biodegradation of organic materials in our environment, particularly plant materials in the form of leaf litter and other plant debris. Such fungi play a vital role in recycling essential elements, particularly carbon.
Figure 18: Basidocarps of wood roting fungus developing on tree stump (From Fungionline).
Fungi are very effective and efficient biodegraders because of the wide range of extracellular enzymes they produce, which are capable of degrading complex polymers, such as cellulose, proteins and lignins. Unfortunately, their excellent biodegradative abilities mean that many saprotrophic fungi are capable of contaminating our food sources or destroying many consumer goods we manufacture from natural raw organic materials. For example, some saprotrophic fungi are particulalry dangerous contaminants of seeds and grains because they produce metabolites known as Mycotoxins (fungal toxins). When ingested mycotoxins cause toxic or carcinogenic symptoms in humans and other animals. Some Aspergillus species produce a group of chemically related mycotoxins called Aflatoxins. A second example is provided by the 'dry rot' fungus, Serpula lacrymans, which attacks wood and can be a very costly, potentially dangerous and certainly most unwelcome visitor when it attacks timbers used in the construction of buildings (e.g. floor and wall joists or roof timbers).
3.2 Fungi are responsible for the majority of plant diseases and several diseases of animals (including humans)
For example, Phytophthora infestans is the causal agent of late blight disease in potatoes. The disease reached epidemic proportions across Europe in the mid 19th century and resulted in the Irish potato famine.
Figure 19: Potato tubers exhibiting symptoms of late blight disease caused by Phytopthora infestans (from Fungionline).
Some fungi are actively parasitic in humans and other animals, while others induce severe allergic reactions if their spores are inhaled - resulting in attacks of asthma or hay-fever.
Figure 20: Symptoms of Ringworm Infection on wrist (From Fungionline).
3.3 Fungi are used in industrial fermentation processes
Yeasts and mycelial fungi are used in a variety of industrial fermentation processes. For example, Saccharomyces species are used extensively in brewing beers and wines, as well as in bread-making.
3.4 Many fungi provide us with a direct source of food
Some yeasts and mycelial fungi are cultured on a large scale and then undergo further processing to provide various protein-rich food products for human or livestock consumption. For example, Quorn™ mycoprotein is produced commercially from the mycelial fungus Fusarium venanatum. The mycelium is harvested and processed to provide a protein-rich meat substitute in a range of convenience foods.
Some species are cultivated for their edible fruiting bodies, e.g. the basidiocarps of Agaricus bisporus.
3.5 Fungi are used in bioremediation
Some species of yeasts and mycelial fungi are used in processes aimed at reducing the concentrations and toxicities of waste materials, particularly from industrial processes, before those wastes are released into the environment - a process known as bioremediation. For example, Aspergillus niger is used to breakdown tannins in tannery effluents to less toxic compounds.
3.6 Some fungi prove highly beneficial in agriculture, horticulture and forestry
For example, some species form symbiotic relationships with the roots of plants, known as MYCORRHIZAS. Mycorrhizas significantly improve plant growth and vigour, resulting in increased yields in crop plants. Other fungal species are used in the biological control of insect and nematode pests, weeds and pathogenic microorganisms. For example, the fungus Beauvaria bassiana is used to control a number of insect pests.
4. Fusarium Species
Fusarium species have been important for many years as plant pathogens causing diseases such as crown rot, head blight, and scab on cereal grains; vascular wilts on a wide range of horticultural crops; root rots; cankers; and other diseases such as pokkah-boeng on sugarcane and bakanae disease of rice. In the last 20 years, Fusarium species have been studied extensively because the mycotoxins they produce can be a threat to animal and human health. Mycotoxins are secondary metabolites produced by fungi that are associated with a variety of animal diseases and some human health problems. More recently, Fusarium species have become important as pathogens of human patients with compromised immune systems. Fusarium species are widely distributed in soil and on subterranean and aerial plant parts, plant debris, and other organic substrates. They are common in tropical and temperate regions and are also found in desert, alpine, and arctic areas, where harsh climatic conditions prevail. Many Fusarium species are abundant in fertile cultivated and rangeland soils but are relatively uncommon in forest soils. Fusarium species are often regarded as soilborne fungi because of their abundance in soil and their frequent association with plant roots, as either parasites or saprophytes. However, many have active or passive means of dispersal in the atmosphere and are common colonizers of aerial plant parts, where they may result in diseases of considerable economic importance. Some of these airborne Fusarium species are encountered rarely in isolations of cultures from soil or roots. The widespread distribution of Fusarium species may be attributed to the ability of these fungi to grow on a wide range of substrates and their efficient mechanisms for dispersal.
4.1 TAXONOMY
Many species, populations within species, and unidentified populations in the genus Fusarium exhibit a remarkable degree of variation with respect to morphological, cultural, and physiological characteristics. This capacity for variation may explain, in part, the ability of Fusarium species to colonize diverse ecological niches in most geographic areas of the world. However, variation has led to considerable difficulties in the development of a stable and widely accepted taxonomic system for the genus. The proliferation in the number of species described prior to 1900 can be attributed in part to variability in many Fusarium populations as well as to inadequate criteria for delimiting taxa. During the last decade, mycologists and plant pathologists have reached a reasonable degree of consensus on the taxonomy of Fusarium species. The basic approach proposed and illustrated by Nelson et al and Burgess et al has been accepted by many workers and is based largely on Die Fusarien . Since 1982, several new species have been recognized and some species have been emended or transferred to another genus [e.g., F. stoveri Booth to Michrodochium stoveri (Booth) Samuels and Hallett]. It is not surprising that additional populations of Fusarium species distinctive enough to be recognized as new taxa have been identified, as it is only in the last 20 years that intensive and extensive surveys of Fusarium populations associated with various crops and soils in the hot semiarid and subtropical regions of the world have been completed (34, 35, 120). Prior to the completion of these surveys, Fusarium taxonomy had been based mainly on material collected in cool temperate regions, although Reinking and Wollenweber, Wollenweber and Reinking, Gordon and Booth did have access to cultures collected from some tropical regions. It is likely that other populations will be differentiated as further systematic surveys of Fusarium species are completed in arid and tropical regions, where information on the nature and distribution of Fusarium populations is limited. The genus Fusarium is divided into sections. A section is used for genera with a large number of species to group species with similar morphological characteristics. In some sections in Fusarium such as Elegans and Spicarioides, there is only one species per section. In other sections, such as Gibbosum and Discolor, there may be five to ten species per section.
4.2 General Characteristics of Fusarium Species
Fusarium species may produce three types of spores called macroconidia, microconidia, and chlamydospores (SubFig. 2 to 13 in Figure 21). Some species produce all three types of spores, while other species do not. The macroconidia are produced in a specialized structure called a sporodochium in which the spore mass is supported by a superficial cushionlike mass of short monophialides bearing the macroconidia (85). The sporodochium sometimes may be encased in slime. Macroconidia may also be produced on monophialides and polyphialides in the aerial mycelium (SubFig. 14 to 20 in Figure 22). A monophialide is a condiophore with only one opening or pore through which endoconidia are extruded, while a polyphialide has two or more such openings or pores. Some conidia are intermediate in size and shape, and these have been referred to as both macroconidia (154) and mesoconidia (168). These intermediate conidia are found primarily in F. semitectum Berk. & Rav., F. avenaceum, and F. subglutinans (Wollenw. & Reinking) Nelson, Toussoun & Marasas. Until more cultures of each species are studied thoroughly, the use of the term mesoconidia is questionable. Microconidia are produced in the aerial mycelium but not in sporodochia. They may be produced in false heads only or in false heads and chains (Fig. 21) on either monophialides or polyphialides. False heads occur when a drop of moisture forms on the tip of the conidiophore and contains the endoconidia as they are produced. Microconidia are of various shapes and sizes (Fig. 22), and those produced in chains have a truncate base (Fig. 22). The third type of spore formed by Fusarium species is a chlamydospore, which is a thick-walled spore filled with lipid like material that serves to carry the fungus over winter in soil when a suitable host is not available. The chlamydospores may be borne singly, in pairs, in clumps, or in chains, and the outer wall may be smooth or rough (Fig. 10 to 12).
Figure 21:SUBFIG. 2-7. Macroconidia of several Fusarium species: 2, F. culmorum; 3, F. solani; 4, F. equiseti; 5, F graminearum; 6, F longipes; 7, F. avenaceumn. Magnification (each), X950.SUBFIG. 8, 9, 13. Microconidia of several Fusarium species: 8, F. scirpi (magnification, x 1,000); 9, F moniliforme (magnification, x 1,000); 13, F solani (magnification, x950). SUBFIG. 10-12. Chlamydospores of several Fusarium species: 10, F. oxysporum; 11, F. equiseti (magnification, x 1,000); 12, F. solani (magnification, x950).()
Figure 22:SUBFIG. 14-17. Monophialides of several Fusarium species: 14, F. poae; 15, F. solani; 16, F. moniliforme; 17, F. oxysporum. Magnification (each), (x970). SUBFIG. 18-20. Polyphialides of several Fusarium species: 18, F. subglutinans; 19, F. scirpi; 20, F. proliferatum. Magnification (each), (X970). SUBFIG. 21. Microconidia of F. moniliforme formed in long chains. Magnification, X109.
4.3 Primary Characters Used To Separate Species in Fusarium Taxonomy
Morphology of the macroconidia. The morphology of the macroconidia is the key characteristic for characterization not only of the species but also of the genus Fusarium. Macroconidia of Fusarium species are of various shapes and sizes (SubFig. 2 to 7), but the shape of the macroconidia formed in sporodochia for a given species is a relatively consistent and stable feature when the fungus is grown on natural substrates under standard conditions (33, 154, 252). Dimensions of the macroconidia may show considerable variation within individual species and should be used cautiously as taxonomic criteria. Microconidia. The presence or absence of microconidia is a primary character in Fusarium taxonomy. If microconidia are present, the features considered are the shape (Fig. 23) and the mode of formation, whether it be singly, in false heads only, or in false heads and chains (SubfigFig. 21). The mode of formation of microconidia is best observed in situ on a natural substrate agar medium such as carnation leaf agar (54). Microconidiophores. The morphology of the conidiophores bearing the microconidia is a primary taxonomic character. These conidiophores may be either monophialides only (SubFig. 14 to 17) or both monophialides and polyphialides (SubFig. 18 to 20) in a given species producing microconidia. Chlamydospores. The presence or absence of chlamydospores is a primary character in Fusanium taxonomy. If chlamydospores are present, they may be formed singly, in pairs, in clumps, or in chains, with either rough or smooth walls.
Figure 23: Shapes of microconidia of various Fusanum species: a, fusiform; b, oval; c, obovoid; d, obovoid with a truncate base indicating that the microconidia were formed in a chain; e, allantoid; f, napiform; g, pyriform; h, turbinate.
4.4 Secondary Characters Useful in Separating Species in Fusarium Taxonomy
The following secondary characteristics are useful in describing a species when the cultures are grown under standard environmental conditions of light, temperature, and substrate (33, 154) but should not be regarded as suitable criteria for differentiation of a species: the morphology and pigmentation of the colony, including the presence or absence of sporodochia, sclerotia, or stroma. The pigmentation of colonies grown on carbohydrate-rich media is variable in some species. The pigmentation of the colony may be helpful to someone with experience in Fusanium taxonomy but quickly can lead those without prior experience in this area astray. The linear growth rate of the fungus under controlled conditions was used as a taxonomic characteristic by Booth (28) and others (33) but must also be used with caution. Isolates within a species may vary considerably with respect to the secondary characters. The degree of variation shown by a particular secondary character may differ between species. Although the shape of the macroconidia formed in sporodochia on carnation leaf agar is a reliable character, the length and width of the macroconidia are less stable features and should be regarded as secondary characters. The macroconidia of a wide range of isolates of F. culmorum (W. G. Smith) Sacc. are relatively uniform in length, whereas the length of macroconidia of F. equiseti (Corda) Sacc. varies widely between isolates, even among those from the same geographic location.
Refrences
http://www.doctorfungus.org/
http://www.mycolog.com/CHAP1.htm
http://www.tolweb.org/Fungi
http://www.ruf.rice.edu/~bioslabs/studies/invertebrates/kingdoms.html
http://www.fungionline.org.uk/1intro/4classification.html
http://www.mycolog.com/CHAP3a.htm
1. Introduction
The really basic division among life forms is between the simpler Prokaryotes and the more complex Eukaryotes. Look at the diagram below: it shows the way in which we think the Kingdoms evolved. It is based on molecular evidence: base sequences from ribosomal RNA.
Figure 1:Evolution of Kingdoms
The earliest forms of life, which appeared about 3,500 - 3,800 million years ago, were prokaryotes. We tend to define them by their relative morphological simplicity, and by the absence of many features found in more modern cells. Although their modern descendants have a single chromosome, this is not found inside a nucleus, and their cytoplasm contains no mitochondria or plastids (cytoplasmic organelles). These organisms make up the baseline Kingdoms Archaebacteria and Eubacteria (These are sometimes called Domains, and regarded as having equal 'rank' with the whole of the Eukaryota). It is also now believed that the earliest cells swapped genes in lateral transfers before the three domains became distinct. Most gene-swapping now takes place within, rather than among, domains, which is one reason they are still recognizable entities.
The prokaryotes had the world to themselves for 1,500 million years (they did, however, invent photosynthesis during that time). Not until about 2 billion years ago did life take the next giant step, the evolution of the eukaryotic cell. Many, perhaps most, biologists now believe that this arose as a result of the mutually beneficial symbiotic union of several different kinds of prokaryote within another host prokaryote. At least two kinds of modern organelle have been found to retain some of their original independent DNA: (1) Mitochondria, which specialize in the oxidation of 3-carbon organic acids (the Krebs cycle), providing an immediately available energy supply in the form of ATP; and (2) Plastids, which may contain photosynthetic pigments and enzymes (chloroplasts), or may store food. Some biologists also think that flagella were once free-living prokaryotes.
Eukaryotic cells also have their DNA organized into a number of discrete chromosomes, which are found inside a membrane-bounded nucleus. Cell division in eukaryotes involves a complex process called mitosis. The nuclear membrane breaks down, a mitotic spindle of microtubules develops, and the chromosomes are duplicated. Then the daughter chromosomes separate and are pulled to opposite poles by the contracting spindle fibres. Each set of chromosomes then becomes enclosed by a new nuclear membrane, and the cell finally divides into two.
Prokaryotic cells have only a single, usually circular chromosome, and do not undergo mitosis. They usually divide by a much simpler process called binary fission. Mitosis, with its very accurate duplication and sharing of the genetic material, seems to have been a crucial invention. Only eukaryotic cells, with their precisely regulated genetic mechanisms, apparently had the potential to evolve into more complex, multicellular organisms in which cells are organized into different tissues and organs. All prokaryotes are still microbes.
Now look at the Kingdom diagram again (above). The Archaebacteria and the Eubacteria are prokaryotes. The eukaryotes encompass the other five Kingdoms, and it is in these other Kingdoms that the dazzling evolutionary explosion of new taxa has occurred. The diagram shows five eukaryote Kingdoms: Protista (now often called Protozoa), Chromista, Plantae, Animalia and Eumycota.
The burst of eukaryote evolution was made possible by, among other things, a modified form of mitosis called meiosis or reduction division. In many organisms this produces special sex cells called gametes. Each of these cells has a single set of chromosomes (we say that the cells are haploid). When two gametes from compatible parent organisms fuse, the resulting cell (the zygote) has two sets of chromosomes (we call this condition diploid). In plants and animals, zygotes develop into diploid, multicellular organisms, but in most fungi the vegetative phase is always haploid, so meiosis must take place in the zygote. Whether meiosis happens in the zygote, or at the other end of the life cycle, during the formation of gametes, it is responsible for the reassortment of the genetic information built into the chromosomes. New features are constantly being added to the pool of genetic material by the process of mutation, but sexual reproduction is the mechanism by which this pool is recombined each generation in most eukaryotic organisms, producing an endless supply of variation upon which the processes of natural selection can work. This is one of the key secrets of eukaryote diversity.
The radiation of the two largely unicellular Kingdoms (Protozoa and Chromista) shows how the evolution of the eukaryotic cell expanded life's horizons. But the full potential of the new teamwork -- we call it that, since several prokaryotes cooperate to make one functional eukaryotic cell -- was not realized until cells, as well as cell components, began to cooperate. When organisms became multicellular, different cells could assume different, specialised functions. This division of labour eventually led to the development of tissues and organs, and ultimately permitted the evolution of complex beings like ourselves, beings with almost infinitely expanded capabilities (both wonderful and terrible).
Three new multicellular Kingdoms arose, exemplifying three different ways of life. Multicellular organisms which could photosynthesize -- make their own food from simple inorganic precursors -- were eaten by other multicellular organisms that lacked this talent, and both were recycled after death by a third group. These groups we call producers, consumers and decomposers -- the plants, the animals and the fungi. We recognize about 9 phyla of plants, about 32 phyla of animals, and 6 phyla of fungi (2 chromistan and 4 eumycotan).
The world being what it is, the picture is not as simple as we might like. Some of the divergent paths of evolution have come together again, almost as they did at the birth of the eukaryotes, and many organisms that seem unitary are in fact partnerships or even consortia. Lichens, for example, always incorporate both an alga (eukaryotic or prokaryotic) and a fungus.
1.1 Five Kingdom Classification System
Once upon a time, all living things were lumped together into two kingdoms, namely plants and animals (at least, that's how I learned it). Animals included every living thing that moved, ate, and grew to a certain size and stopped growing. Plants included every living thing that did not move or eat and that continued to grow throughout life. It became very difficult to group some living things into one or the other, so early in the past century the two kingdoms were expanded into five kingdoms: Protista (the single-celled eukaryotes); Fungi (fungus and related organisms); Plantae (the plants); Animalia (the animals); Monera (the prokaryotes). Many biologists now recognize six distinct kingdoms, dividing Monera into the Eubacteria and Archeobacteria.
All I can say is that the sytem holds true for this week, at least. It might even hold up for a century or two. Accepted systems of classification have changed at a far faster pace than the species have taken to evolve, that's for certain.
Kingdoms are divided into categories called phyla, each phylum is divided into classes, each class into orders, each order into families, each family into genera, and each genus into species. A species represents one type of organism, such as dog, tiger shark, Ameoba proteus (the common amoeba), Homo sapiens (us), or Acer palmatum (Japanese maple). Note that species names should be underlined or written in italics.
Classifying larger organisms into kingdoms is usually easy, but in a microenvironment it can be tricky. If you have had a little biology, a good exercise is to describe individual living things, and to try to classify them as to kingdom.
1.1.1 Kingdom Monera (includes Eubacteria and Archeobacteria)
Individuals are single-celled, may or may not move, have a cell wall, have no chloroplasts or other organelles, and have no nucleus. Monera are usually very tiny, although one type, namely the blue-green bacteria, look like algae. They are filamentous and quite long, green, but have no visible structure inside the cells. No visible feeding mechanism. They absorb nutrients through the cell wall or produce their own by photosynthesis.
1.1.2 Kingdom Protista
Protists are single-celled and usually move by cilia, flagella, or by amoeboid mechanisms. There is usually no cell wall, although some forms may have a cell wall. They have organelles including a nucleus and may have chloroplasts, so some will be green and others won't be. They are small, although many are big enough to be recognized in a dissecting microscope or even with a magnifying glass. Nutrients are acquired by photosynthesis, ingestion of other organisms, or both.
1.1.3 Kingdom Fungi
Fungi are multicellular,with a cell wall, organelles including a nucleus, but no chloroplasts. They have no mechanisms for locomotion. Fungi range in size from microscopic to very large ( such as mushrooms). Nutrients are acquired by absorption. For the most part, fungi acquire nutrients from decaying material.
1.1.4 Kingdom Plantae
Plants are multicellular and most don't move, although gametes of some plants move using cilia or flagella. Organelles including nucleus, chloroplasts are present, and cell walls are present. Nutrients are acquired by photosynthesis (they all require sunlight).
1.1.5 Kingdom Animalia
Animals are multicellular, and move with the aid of cilia, flagella, or muscular organs based on contractile proteins. They have organelles including a nucleus, but no chloroplasts or cell walls. Animals acquire nutrients by ingestion.
2. Kingdom Fungi
The organisms of the fungal lineage include mushrooms, rusts, smuts, puffballs, truffles, morels, molds, and yeasts, as well as many less well-known organisms. More than 70,000 species of fungi have been described; however, some estimates of total numbers suggest that 1.5 million species may exist.
As the sister group of animals and part of the eukaryotic crown group that radiated about a billion years ago, the fungi constitute an independent group equal in rank to that of plants and animals. They share with animals the ability to export hydrolytic enzymes that break down biopolymers, which can be absorbed for nutrition. Rather than requiring a stomach to accomplish digestion, fungi live in their own food supply and simply grow into new food as the local environment becomes nutrient depleted.
Most biologists have seen dense filamentous fungal colonies growing on rich nutrient agar plates, but in nature the filaments can be much longer and the colonies less dense. When one of the filaments contacts a food supply, the entire colony mobilizes and reallocates resources to exploit the new food. Should all food become depleted, sporulation is triggered. Although the fungal filaments and spores are microscopic, the colony can be very large with individuals of some species rivaling the mass of the largest animals or plants.
Figure 2: Hyphae of a wood-decaying fungus found growing on the underside of a fallen log. The metabolically active hyphae have secreted droplets on their surfaces. Copyright © M. Blackwell 1996.
Prior to mating in sexual reproduction, individual fungi communicate with other individuals chemically via pheromones. In every phylum at least one pheromone has been characterized, and they range from sesquiterpines and derivatives of the carotenoid pathway in chytridiomycetes and zygomycetes to oligopeptides in ascomycetes and basidiomycetes.
Within their varied natural habitats fungi usually are the primary decomposer organisms present. Many species are free-living saprobes (users of carbon fixed by other organisms) in woody substrates, soils, leaf litter, dead animals, and animal exudates. The large cavities eaten out of living trees by wood-decaying fungi provide nest holes for a variety of animals, and extinction of the ivory billed woodpecker was due in large part to loss, through human activity, of nesting trees in bottom land hardwoods. In some low nitrogen environments several independent groups of fungi have adaptations such as nooses and sticky knobs with which to trap and degrade nematodes and other small animals. A number of references on fungal ecology are available.
However, many other fungi are biotrophs, and in this role a number of successful groups form symbiotic associations with plants (including algae), animals (especially arthropods), and prokaryotes. Examples are lichens, mycorrhizae, and leaf and stem endophytes. Although lichens may seem infrequent in polluted cities, they can form the dominant vegetation in nordic environments, and there is a better than 80% chance that any plant you find is mycorrhizal. Leaf and stem endophytes are a more recent discovery, and some of these fungi can protect the plants they inhabit from herbivory and even influence flowering and other aspects of plant reproductive biology. Fungi are our most important plant pathogens, and include rusts, smuts, and many ascomycetes such as the agents of Dutch elm disease and chestnut blight. Among the other well known associations are fungal parasites of animals. Humans, for example, may succumb to diseases caused by Pneumocystis (a type of pneumonia that affects individuals with supressed immune systems), Coccidioides (valley fever), Ajellomyces (blastomycosis and histoplasmosis), and Cryptococcus (cryptococcosis).
Figure 3: The fluffy white hyphae of the mycorrhizal fungus Rhizopogon rubescens has enveloped the smaller roots of a Virginia pine seedling. Note that some of the mycelium extends out into the surrounding environment. Copyright © J. B. Anderson 1996.
Figure 4: Entomophthora, "destroyer of insects", is the agent of a fungual infection that kills flies. After their death the fungal growth erupts through the fly cuticle, and dispersal by forcible spore discharge is a source of inoculum for infection of new flies. Copyright © G. L. Barron 1996.
Fungal spores may be actively or passively released for dispersal by several effective methods. The air we breathe is filled with spores of species that are air dispersed. These usually are species that produce large numbers of spores, and examples include many species pathogenic on agricultural crops and trees. Other species are adapted for dispersal within or on the surfaces of animals (particularly arthropods). Some fungi are rain splash or flowing water dispersed. In a few cases the forcible release of spores is sufficient to serve as the dispersal method as well. The function of some spores is not primarily for dispersal, but to allow the organisms to survive as resistant cells during periods when the conditions of the environment are not conducive to growth.
Figure 5: Diversity of Spores among Fungi.
Fungi are vital for their ecosystem functions, some of which we have reviewed in the previous paragraphs. In addition a number of fungi are used in the processing and flavoring of foods (baker's and brewer's yeasts, Penicillia in cheese-making) and in production of antibiotics and organic acids. Other fungi produce secondary metabolites such as aflatoxins that may be potent toxins and carcinogens in food of birds, fish, humans, and other mammals.
A few species are studied as model organisms that can be used to gain knowledge of basic processes such as genetics, physiology, biochemistry, and molecular biology with results that are applicable to many organisms. Some of the fungi that have been intensively studied in this way include Saccharomyces cereviseae, Neurospora crassa, and Ustilago maydis.
Most phyla appear to be terrestrial in origin, although all major groups have invaded marine and freshwater habitats. An exception to this generality is the flagellum-bearing phyla Chytridiomycota, Blastocladiomycota, and Neocallimastigomycota (collectively referred to as chytrids), which probably had an aquatic origin. Extant chytrid species also occur in terrestrial environments as plant pathogenic fungi, soil fungi, and even as anaerobic inhabitants of the guts of herbivores such as cows (all Neocallimastigomycota).
2.1 Characteristics
Fungi are characterized by non-motile bodies (thalli) constructed of apically elongating walled filaments (hyphae), a life cycle with sexual and asexual reproduction, usually from a common thallus, haploid thalli resulting from zygotic meiosis, and heterotrophic nutrition. Spindle pole bodies, not centrioles, usually are associated with the nuclear envelope during cell division. The characteristic wall components are chitin (beta-1,4-linked homopolymers of N-acetylglucosamine in microcrystalline state) and glucans primarily alpha-glucans (alpha-1,3- and alpha-1,6- linkages).
Figure 6: Portion of a hypha of a zygomycete stained with a blue dye to show the many nuclei present. Many other fungi have septations that devide the hyphae into compartments that usually contain one to several nuclei per compartment. Copyright © M. Blackwell 1996.
Figure 7: Transmission electron micrograph showing duplicated spindle pole body of a prophase I meiotic nucleus of a basidiomycete Exobasidium. Only chytrids among fungi have centrioles and lack spindle pole bodies. Copyright © Beth Richardson 1996.
Exceptions to this characterization of fungi are well known, and include the following: Most species of chytrids have cells with a single, smooth, posteriorly inserted flagellum at some stage in the life cycle, and centrioles are associated with nuclear division. The life cycles of most chytrids are poorly studied, but some (Blastocladiomycota) are known to have zygotic meiosis (therefore, alternation between haploid and diploid generations). Certain members of Mucoromycotina, Ascomycota, and Basidiomycota may lack hyphal growth during part or all of their life cycles, and, instead, produce budding yeast cells. Most fungal species with yeast growth forms contain only minute amounts of chitin in the walls of the yeast cells. A few species of Ascomycota (Ophiostomataceae) have cellulose in their walls, and certain members of Blastocladiomycota and Entomophthoromycotina lack walls during part of their life cycle.
2.2 Fossil Record
Based on the available fossil record, fungi are presumed to have been present in Late Proterozoic (900-570 mya). Terrestrial forms of purported ascomycetes are reported in associations with microarthropods in the Silurian Period (438-408 mya). Fossil hyphae in association with wood decay and fossil chytrids and Glomales-Endogonales representatives associated with plants of the Rhynie Chert are reported from the Devonian Period (408-360 mya). Fungal fossil diversity increased throughout the Paleozoic Era with all modern classes reported in the Pennsylvanian Epoch (320-286 mya).
A first attempt to match molecular data on fungal phylogeny to the geological record shows general agreement, but does point out some conflicts between the two types of data.
2.4 Biogeography
Wherever adequate moisture, temperature, and organic substrates are available, fungi are present. Although we normally think of fungi as growing in warm, moist forests, many species occur in habitats that are cold, periodically arid, or otherwise seemingly inhospitable. It is important to recognize that optimum conditions for growth and reproduction vary widely with fungal species. Diversity of most groups of fungi tends to increase in tropical regions, but detailed studies are only in their infancy .
Although many saprobic and plant pathogenic species with low substrate specificity and effective dispersal systems have broad distributions, gene flow appears to be restricted in many fungi. For these species large bodies of water such as the Atlantic and Pacific Oceans create barriers to gene exchange. Some distributions are limited by substrate availability, and dramatic examples come from parasites of Gondowanan plants; one of these is the Southern Hemisphere distribution of the ascomycete Cyttaria, corresponding with part of the distribution of its host plant Nothofagus. The fossil record shows that fungi were present in Antarctica, as is the case for other organisms with Gondwanan distributions. Arthropod associates also may show distributions throughout part or all of a host range, and some fungal species (ex. wood wasp associates) occur outside the range of the associated arthropod.
2.5 Kingdom Fungi Classification
All living things can be classified into one of five fundamental Kingdoms of life, and the term fungus refers generically to all members of the Kingdom Fungi. There are more than a million species of fungi, but only about 400 cause diseases relevant to man, animals, or plants. The majority of the pathogenic species are classified within the Phyla Zygomycota, Basidiomycota, Ascomycota, or the form group Fungi Imperfecti. Fungi (the singular form is 'fungus'), including those pathogenic to humans and animals, are eukaryotic microorganisms.
Figure 8: Classification of Fungi.
2.5.1 Phylogeny Based Classification
Figure 9: Phylogeny modified from James et al., 2006a, 2006b; Liu et al., 2006; Seif et al., 2005; Steenkamp et al., 2006.
2.5.1.1 Basidomycota
The Basidiomycota contains about 30,000 described species, which is 37% of the described species of true Fungi. The most conspicuous and familiar Basidiomycota are those that produce mushrooms, which are sexual reproductive structures. The Basidiomycota also includes yeasts (single-celled forms; Fell et al. 2001) and asexual species. Basidiomycota are found in virtually all terrestrial ecosystems, as well as freshwater and marine habitats.
Basidiomycota have a huge impact on human affairs and ecosystem functioning. Many Basidiomycota obtain nutrition by decaying dead organic matter, including wood and leaf litter. Thus, Basidiomycota play a significant role in the carbon cycle. Unfortunately, Basidiomycota frequently attack the wood in buildings and other structures, which has negative economic consequences for humans.
Symbiotic lifestyles (intimate associations with other living organisms) are well developed in the Basidiomycota. Symbiotic Basidiomycota include important plant pathogens, such as "rusts" (Uredinales) and "smuts" (Ustilaginales), which attack wheat and other crops. Other symbiotic Basidiomycota cause diseases in animals, including humans. Not all symbiotic Basidiomycota cause obvious harm to their partners, however. For example, some Basidiomycota, as well as a handful of Ascomycota, form ectomycorrhizae, which are associations with the roots of vascular plants (principally forest trees such as oaks, pines, dipterocarps, and eucalypts. Ectomycorrhizal Basidiomycota help their plant partners obtain mineral nutrients from the soil, and in return they receive sugars that the plants produce through photosynthesis. Other symbiotic Basidiomycota form associations with insects, including leaf-cutter ants, termites, scale insects, woodwasps, and bark beetles.
Humans have found diverse uses for Basidiomycota. Mushrooms, both cultivated and wild, are eaten in many countries. For the untrained, mushroom-hunting is a risky endeavor, because some Basidiomycota produce deadly toxins. The basidiomycete toxin phalloidin (from the mushroom Amanita phalloides) binds actin, which is a component of microfilaments. Fluorescent stains that incorporate phalloidin are used by cell biologists to visualize the cytoskeleton. Other "toxins" produced by Basidiomycota include hallucinogens, which are produced by members of the genus Psilocybe (and other groups). Species of Psilocybe have traditionally been used in Central American indigenous cultures as a spiritual tool, and are now cultivated for the illicit drug trade. Other biochemical compounds of Basidiomycota that have practical uses include astaxanthin, a red pigment produced by the basidiomycetous yeast Phaffia (used to add color to farmed salmon), and certain enzymes from wood-decaying Basidiomycota that have potential applications in paper production and bioremediation (decontamination of polluted environments using biological agents).
Figure 10: SEM of the surface of a mushroom gill (Coprinus cinereus: Agaricomycotina) showing several basidia, some with four basidiospores attached.(From McLaughlin, et al. 1985; used with permission © McLaughlin, Beckett and Yoon 1985.)
2.5.1.2 Ascomycota
The Ascomycota, or sac fungi, is monophyletic and accounts for approximately 75% of all described fungi. It includes most of the fungi that combine with algae to form lichens, and the majority of fungi that lack morphological evidence of sexual reproduction. Among the Ascomycota are some famous fungi: Saccharomyces cerevisiae, the yeast of commerce and foundation of the baking and brewing industries (not to mention molecular developmental biology), Penicillium chrysogenum, producer of penicillin, Morchella esculentum, the edible morel, and Neurospora crassa, the "one-gene-one-enzyme" organism. There are also some infamous Ascomycota, a few of the worst being: Aspergillus flavus, producer of aflatoxin, the fungal contaminant of nuts and stored grain that is both a toxin and the most potent known natural carcinogen, Candida albicans, cause of thrush, diaper rash and vaginitis, and Cryphonectria parasitica, responsible for the demise of 4 billion chestnut trees in the eastern USA.Asexual Ascomycota, such as Penicillium or Candida species, used to be classified separately in the Deuteromycota because sexual characters were necessary for Ascomycota classification. However, the comparison of nucleic acid sequence, as well as nonsexual phenotypic characters, have permitted the integration of asexual fungi into the Ascomycota. The Deuteromycota is no longer recognized as a formal taxon in fungal systematics.
Figure 11: In hyphal Ascomycota, the youngest, terminal hyphal segments develop into 8-spored asci. Asci of a hyphal Ascomycota (Pezizomycotina), Podospora , © R. Vilgalys 1996. Ascus of a yeast (Saccharomycotina), Saccharomyces, © J. Taylor 1996.
2.5.1.3 Glomeromycota
Although the Glomeromycota comprise a group of fungi virtually unknown to the broad public, they are essential for terrestrial ecosystem function. Members of this group are mutualistic symbionts that form arbuscular mycorrhizal (AM) associations intracellularly within the roots of the vast majority of herbaceous plants and tropical trees. This type of symbiosis is termed mutualistic because the fungus and host plant both benefit from this intimate association. The fungal symbiont receives carbohydrates from the plant in exchange for functioning as an extended root system, thereby dramatically improving mineral uptake by the plant roots. Although there are various types of mycorrhizas, involving different fungal and plant symbionts, the arbuscular mycorrhiza type is the most widespread. The phylum Glomeromycota currently comprises approximately 150 described species distributed among ten genera, most of which are defined primarily by spore morphology. Recently, DNA sequences have also been used to circumscribe taxa.
Figure 12: Spores of Scutellospora castanea (isolate BEG1, photo © Annemarie Brennwald). Spore diameter approximately 220 µm.
2.5.1.4 Zygomycota
The Zygomycota contains approximately 1% of the described species of true Fungi (~900 described species; Kirk et al. 2001). The most familiar representatives include the fast-growing molds that we encounter on spoiled strawberries (Figure 1) and other fruits high in sugar content. Although these fungi are common in terrestrial and aquatic ecosystems, they are rarely noticed by humans because they are of microscopic size. Colonial growth and the taxonomically informative asexual reproductive structures Zygomycota produce are typically studied after culturing on various agar media. Direct microscopic observation of suitable substrates is required for those species that either have not or cannot be cultured. Fewer than half of the species have been cultured and the majority of these are members of the Mucorales, a group that includes some of the fastest growing fungi.
Click on an image to view larger version & data in a new window
Figure 13: Moldy strawberries covered with Rhizopus mycelium. Photo K. O'Donnell.
Zygomycota are defined and distinguished from all other fungi by sexual reproduction via zygospores following gametangial fusion (Figure 14A,B) and asexual reproduction by uni-to-multispored sporangia (Figure 15A,B) within which nonmotile, single-celled sporangiospores are produced. The phylum comprises at least seven phylogenetically diverse orders. Monophyly of the phylum and interrelationships among orders are currently under intensive investigation using multilocus DNA sequence data. This introduction to the Zygomycota does not include the order comprising the arbuscular mycorrhizal (AM) fungi, the Glomales, because it has been elevated to the rank of phylum, the Glomeromycota (Schüßler et al. 2001). One other group, the Microsporidia, were previously considered protozoa, however, DNA, biochemistry, and morphology suggest these highly reduced, obligate, intracellular parasites may have evolved from a zygomycete-like ancestor.
Click on an image to view larger version & data in a new window
Figure 14: Sexual reproduction. (A) Scanning electron micrograph of gametangial fusion in Mucor mucedo. (B) Highly ornamented zygosporangium of Mycotypha africana. (From O'Donnell 1979).
Figure 15: Asexual reproduction. (A) Scanning electron micrograph of unispored sporangia of Benjaminiella poitrasii and (B) dehisced multispored sporangium of Gilbertella persicaria releasing sporangiospores. (From O'Donnell 1979).
Zygomycota are arguably the most ecologically diverse group of fungi, functioning as saprophytes on substrates such as fruit, soil, and dung (Mucorales), as harmless inhabitants of arthropod guts (Harpellales), as plant mutualists forming ectomycorrhizae (Endogonales), and as pathogens of animals, plants, amoebae, and especially other fungi (all Dimargaritales and some Zoopagales are mycoparasites). A number of species are used in Asian food fermentations, such as Rhizopus oligosporus in the Indonesian staple tempeh, and Actinomucor elegans in Chinese cheese or sufu.
Conversely, some species have a negative economic impact on human affairs by causing storage rots of fruits (particularly strawberries by Rhizopus stolonifer [Figure 13]), as agents of plant disease (e.g., Choanephora cucurbitarum flower rot of curcurbits), while other species can cause life-threatening opportunistic infections of diabetic, immuno-suppressed, and immuno-compromised patients. In addition to some Mucorales that attack immuno-suppressed humans, several species of microsporidia cause serious human infections. Some zygomycetes are regularly isolated by veterinarians from domesticated animals in tropical and subtropical regions of the world, including the US gulf states.
2.5.1.5 Blastocladiomycota
The Blastocladiomycota were previously considered a taxonomic clade within the Chytridiomycota. Recent molecular data and ultrastructural characteristics, however, place the Blastocladiomycota as a sister clade to the Zygomycota, Glomeromycota, and Dikarya (Ascomycota and Basiomycota). The blastocladiomycetes are fungi that are saprotrophs and parasites of all eukaryotic groups and undergo sporic meiosis unlike their close relatives, the chytrids, which mostly exhibit zygotic meiosis.
Figure 16: Blastocladiella asperosperma
2.5.1.6 Chytridiomycota
The Phylum Chytridiomycota (chytrids) includes two classes, Chytridiomycetes and Monoblepharidomycetes, each of which is monophyletic based on molecular analyses. Because of their genetic and morphological divergence, two groups of zoosporic fungi once included among chytrids are now classified as separate Phyla, Blastocladiomycota and Neocallimastigomycota. The Chytridiomycetes are currently separated into five orders [Chytridiales , Rhizophydiales , Spizellomycetales, Rhizophlyctidales, and Lobulomycetales] . Molecular phylogenetic analyses have demonstrated that each of these orders is monophyletic, except for the current circumscription of the Chytridiales. Work is progressing on characterization of clades for groups formerly included in the Chytridiales. These groups, which do not cluster with recognized members of the Chytridiales, are listed here as provisional orders. Molecular analyses place two genera assigned to the Spizellomycetales outside of the core chytrid clade. The genus Rozella appears basal to the core chytrids and Olpidium brassicae radiates among zygomycetes. Thus, their classification is uncertain at this time (incertae sedis).
Figure 17: Catenochytridium sp.on Eriocaulon
2.5.1.7 Neocallimastigomycota
The Neocallimastigomycota were earlier placed in the phylum Chytridomycota. Members of this small phylum are anaerobic organisms, living in the digestive system of larger herbivorous mammals and possibly in other terrestrial and aquatic environments. They lack mitochondria but contain hydrogenosomes of mitochondrial origin. As the related chrytrids, neocallimastigomycetes form zoospores that are posteriorly uniflagellate or polyflagellate.
3. Importance of Fungi
3.1 Fungi are agents of biodegradation and biodeterioration
Saprotropic fungi utilise dead organic materials as sources of nutrients and are responsible for the biodegradation of organic materials in our environment, particularly plant materials in the form of leaf litter and other plant debris. Such fungi play a vital role in recycling essential elements, particularly carbon.
Figure 18: Basidocarps of wood roting fungus developing on tree stump (From Fungionline).
Fungi are very effective and efficient biodegraders because of the wide range of extracellular enzymes they produce, which are capable of degrading complex polymers, such as cellulose, proteins and lignins. Unfortunately, their excellent biodegradative abilities mean that many saprotrophic fungi are capable of contaminating our food sources or destroying many consumer goods we manufacture from natural raw organic materials. For example, some saprotrophic fungi are particulalry dangerous contaminants of seeds and grains because they produce metabolites known as Mycotoxins (fungal toxins). When ingested mycotoxins cause toxic or carcinogenic symptoms in humans and other animals. Some Aspergillus species produce a group of chemically related mycotoxins called Aflatoxins. A second example is provided by the 'dry rot' fungus, Serpula lacrymans, which attacks wood and can be a very costly, potentially dangerous and certainly most unwelcome visitor when it attacks timbers used in the construction of buildings (e.g. floor and wall joists or roof timbers).
3.2 Fungi are responsible for the majority of plant diseases and several diseases of animals (including humans)
For example, Phytophthora infestans is the causal agent of late blight disease in potatoes. The disease reached epidemic proportions across Europe in the mid 19th century and resulted in the Irish potato famine.
Figure 19: Potato tubers exhibiting symptoms of late blight disease caused by Phytopthora infestans (from Fungionline).
Some fungi are actively parasitic in humans and other animals, while others induce severe allergic reactions if their spores are inhaled - resulting in attacks of asthma or hay-fever.
Figure 20: Symptoms of Ringworm Infection on wrist (From Fungionline).
3.3 Fungi are used in industrial fermentation processes
Yeasts and mycelial fungi are used in a variety of industrial fermentation processes. For example, Saccharomyces species are used extensively in brewing beers and wines, as well as in bread-making.
3.4 Many fungi provide us with a direct source of food
Some yeasts and mycelial fungi are cultured on a large scale and then undergo further processing to provide various protein-rich food products for human or livestock consumption. For example, Quorn™ mycoprotein is produced commercially from the mycelial fungus Fusarium venanatum. The mycelium is harvested and processed to provide a protein-rich meat substitute in a range of convenience foods.
Some species are cultivated for their edible fruiting bodies, e.g. the basidiocarps of Agaricus bisporus.
3.5 Fungi are used in bioremediation
Some species of yeasts and mycelial fungi are used in processes aimed at reducing the concentrations and toxicities of waste materials, particularly from industrial processes, before those wastes are released into the environment - a process known as bioremediation. For example, Aspergillus niger is used to breakdown tannins in tannery effluents to less toxic compounds.
3.6 Some fungi prove highly beneficial in agriculture, horticulture and forestry
For example, some species form symbiotic relationships with the roots of plants, known as MYCORRHIZAS. Mycorrhizas significantly improve plant growth and vigour, resulting in increased yields in crop plants. Other fungal species are used in the biological control of insect and nematode pests, weeds and pathogenic microorganisms. For example, the fungus Beauvaria bassiana is used to control a number of insect pests.
4. Fusarium Species
Fusarium species have been important for many years as plant pathogens causing diseases such as crown rot, head blight, and scab on cereal grains; vascular wilts on a wide range of horticultural crops; root rots; cankers; and other diseases such as pokkah-boeng on sugarcane and bakanae disease of rice. In the last 20 years, Fusarium species have been studied extensively because the mycotoxins they produce can be a threat to animal and human health. Mycotoxins are secondary metabolites produced by fungi that are associated with a variety of animal diseases and some human health problems. More recently, Fusarium species have become important as pathogens of human patients with compromised immune systems. Fusarium species are widely distributed in soil and on subterranean and aerial plant parts, plant debris, and other organic substrates. They are common in tropical and temperate regions and are also found in desert, alpine, and arctic areas, where harsh climatic conditions prevail. Many Fusarium species are abundant in fertile cultivated and rangeland soils but are relatively uncommon in forest soils. Fusarium species are often regarded as soilborne fungi because of their abundance in soil and their frequent association with plant roots, as either parasites or saprophytes. However, many have active or passive means of dispersal in the atmosphere and are common colonizers of aerial plant parts, where they may result in diseases of considerable economic importance. Some of these airborne Fusarium species are encountered rarely in isolations of cultures from soil or roots. The widespread distribution of Fusarium species may be attributed to the ability of these fungi to grow on a wide range of substrates and their efficient mechanisms for dispersal.
4.1 TAXONOMY
Many species, populations within species, and unidentified populations in the genus Fusarium exhibit a remarkable degree of variation with respect to morphological, cultural, and physiological characteristics. This capacity for variation may explain, in part, the ability of Fusarium species to colonize diverse ecological niches in most geographic areas of the world. However, variation has led to considerable difficulties in the development of a stable and widely accepted taxonomic system for the genus. The proliferation in the number of species described prior to 1900 can be attributed in part to variability in many Fusarium populations as well as to inadequate criteria for delimiting taxa. During the last decade, mycologists and plant pathologists have reached a reasonable degree of consensus on the taxonomy of Fusarium species. The basic approach proposed and illustrated by Nelson et al and Burgess et al has been accepted by many workers and is based largely on Die Fusarien . Since 1982, several new species have been recognized and some species have been emended or transferred to another genus [e.g., F. stoveri Booth to Michrodochium stoveri (Booth) Samuels and Hallett]. It is not surprising that additional populations of Fusarium species distinctive enough to be recognized as new taxa have been identified, as it is only in the last 20 years that intensive and extensive surveys of Fusarium populations associated with various crops and soils in the hot semiarid and subtropical regions of the world have been completed (34, 35, 120). Prior to the completion of these surveys, Fusarium taxonomy had been based mainly on material collected in cool temperate regions, although Reinking and Wollenweber, Wollenweber and Reinking, Gordon and Booth did have access to cultures collected from some tropical regions. It is likely that other populations will be differentiated as further systematic surveys of Fusarium species are completed in arid and tropical regions, where information on the nature and distribution of Fusarium populations is limited. The genus Fusarium is divided into sections. A section is used for genera with a large number of species to group species with similar morphological characteristics. In some sections in Fusarium such as Elegans and Spicarioides, there is only one species per section. In other sections, such as Gibbosum and Discolor, there may be five to ten species per section.
4.2 General Characteristics of Fusarium Species
Fusarium species may produce three types of spores called macroconidia, microconidia, and chlamydospores (SubFig. 2 to 13 in Figure 21). Some species produce all three types of spores, while other species do not. The macroconidia are produced in a specialized structure called a sporodochium in which the spore mass is supported by a superficial cushionlike mass of short monophialides bearing the macroconidia (85). The sporodochium sometimes may be encased in slime. Macroconidia may also be produced on monophialides and polyphialides in the aerial mycelium (SubFig. 14 to 20 in Figure 22). A monophialide is a condiophore with only one opening or pore through which endoconidia are extruded, while a polyphialide has two or more such openings or pores. Some conidia are intermediate in size and shape, and these have been referred to as both macroconidia (154) and mesoconidia (168). These intermediate conidia are found primarily in F. semitectum Berk. & Rav., F. avenaceum, and F. subglutinans (Wollenw. & Reinking) Nelson, Toussoun & Marasas. Until more cultures of each species are studied thoroughly, the use of the term mesoconidia is questionable. Microconidia are produced in the aerial mycelium but not in sporodochia. They may be produced in false heads only or in false heads and chains (Fig. 21) on either monophialides or polyphialides. False heads occur when a drop of moisture forms on the tip of the conidiophore and contains the endoconidia as they are produced. Microconidia are of various shapes and sizes (Fig. 22), and those produced in chains have a truncate base (Fig. 22). The third type of spore formed by Fusarium species is a chlamydospore, which is a thick-walled spore filled with lipid like material that serves to carry the fungus over winter in soil when a suitable host is not available. The chlamydospores may be borne singly, in pairs, in clumps, or in chains, and the outer wall may be smooth or rough (Fig. 10 to 12).
Figure 21:SUBFIG. 2-7. Macroconidia of several Fusarium species: 2, F. culmorum; 3, F. solani; 4, F. equiseti; 5, F graminearum; 6, F longipes; 7, F. avenaceumn. Magnification (each), X950.SUBFIG. 8, 9, 13. Microconidia of several Fusarium species: 8, F. scirpi (magnification, x 1,000); 9, F moniliforme (magnification, x 1,000); 13, F solani (magnification, x950). SUBFIG. 10-12. Chlamydospores of several Fusarium species: 10, F. oxysporum; 11, F. equiseti (magnification, x 1,000); 12, F. solani (magnification, x950).()
Figure 22:SUBFIG. 14-17. Monophialides of several Fusarium species: 14, F. poae; 15, F. solani; 16, F. moniliforme; 17, F. oxysporum. Magnification (each), (x970). SUBFIG. 18-20. Polyphialides of several Fusarium species: 18, F. subglutinans; 19, F. scirpi; 20, F. proliferatum. Magnification (each), (X970). SUBFIG. 21. Microconidia of F. moniliforme formed in long chains. Magnification, X109.
4.3 Primary Characters Used To Separate Species in Fusarium Taxonomy
Morphology of the macroconidia. The morphology of the macroconidia is the key characteristic for characterization not only of the species but also of the genus Fusarium. Macroconidia of Fusarium species are of various shapes and sizes (SubFig. 2 to 7), but the shape of the macroconidia formed in sporodochia for a given species is a relatively consistent and stable feature when the fungus is grown on natural substrates under standard conditions (33, 154, 252). Dimensions of the macroconidia may show considerable variation within individual species and should be used cautiously as taxonomic criteria. Microconidia. The presence or absence of microconidia is a primary character in Fusarium taxonomy. If microconidia are present, the features considered are the shape (Fig. 23) and the mode of formation, whether it be singly, in false heads only, or in false heads and chains (SubfigFig. 21). The mode of formation of microconidia is best observed in situ on a natural substrate agar medium such as carnation leaf agar (54). Microconidiophores. The morphology of the conidiophores bearing the microconidia is a primary taxonomic character. These conidiophores may be either monophialides only (SubFig. 14 to 17) or both monophialides and polyphialides (SubFig. 18 to 20) in a given species producing microconidia. Chlamydospores. The presence or absence of chlamydospores is a primary character in Fusanium taxonomy. If chlamydospores are present, they may be formed singly, in pairs, in clumps, or in chains, with either rough or smooth walls.
Figure 23: Shapes of microconidia of various Fusanum species: a, fusiform; b, oval; c, obovoid; d, obovoid with a truncate base indicating that the microconidia were formed in a chain; e, allantoid; f, napiform; g, pyriform; h, turbinate.
4.4 Secondary Characters Useful in Separating Species in Fusarium Taxonomy
The following secondary characteristics are useful in describing a species when the cultures are grown under standard environmental conditions of light, temperature, and substrate (33, 154) but should not be regarded as suitable criteria for differentiation of a species: the morphology and pigmentation of the colony, including the presence or absence of sporodochia, sclerotia, or stroma. The pigmentation of colonies grown on carbohydrate-rich media is variable in some species. The pigmentation of the colony may be helpful to someone with experience in Fusanium taxonomy but quickly can lead those without prior experience in this area astray. The linear growth rate of the fungus under controlled conditions was used as a taxonomic characteristic by Booth (28) and others (33) but must also be used with caution. Isolates within a species may vary considerably with respect to the secondary characters. The degree of variation shown by a particular secondary character may differ between species. Although the shape of the macroconidia formed in sporodochia on carnation leaf agar is a reliable character, the length and width of the macroconidia are less stable features and should be regarded as secondary characters. The macroconidia of a wide range of isolates of F. culmorum (W. G. Smith) Sacc. are relatively uniform in length, whereas the length of macroconidia of F. equiseti (Corda) Sacc. varies widely between isolates, even among those from the same geographic location.
Refrences
http://www.doctorfungus.org/
http://www.mycolog.com/CHAP1.htm
http://www.tolweb.org/Fungi
http://www.ruf.rice.edu/~bioslabs/studies/invertebrates/kingdoms.html
http://www.fungionline.org.uk/1intro/4classification.html
http://www.mycolog.com/CHAP3a.htm
Subscribe to:
Posts (Atom)
