What are Fungi?

The Kingdom Fungi includes some of the most important organisms, both in terms of their ecological and economic roles. By breaking down dead organic material, they continue the cycle of nutrients through ecosystems. In addition, most vascular plants could not grow without the symbiotic fungi, or mycorrhizae, that inhabit their roots and supply essential nutrients. Other fungi provide numerous drugs (such as penicillin and other antibiotics), foods like mushrooms, truffles and morels, and the bubbles in bread, champagne, and beer.

Oldest known fungi

The oldest fossil fungi so far known are probably chytrid-like forms from the Vendian Period (Late Precambrian), found in north Russia. Older fossils of Precambrian "fungi" are now usually considered to be empty sheaths of filamentous cyanobacteria, or else are not distinct enough to be placed in any taxon with certainty. Fossil fungi older than the Devonian are rare; the fungi may have undergone an evolutionary radiation at about the same time that the land plants began to radiate.

Classification of fungi

Fungi are usually classified in four divisions: the Chytridiomycota (chytrids), Zygomycota (bread molds), the Basidiomycota (club fungi). Placement into a division is based on the way in which the fungus reproduces sexually. The shape and internal structure of the sporangia, which produce the spores, are the most useful character for identifying these various major groups.

There are also two conventional groups which are not recognized as formal taxonomic groups (ie. they are polyphyletic); these are the Deuteromycota (fungi imperfecti), and the lichens. The Deuteromycota includes all fungi which have lost the ability to reproduce sexually. As a result, it is not known for certain into which group they should be placed, and thus the Deuteromycota becomes a convenient place to dump them until someone gets around to working out their biology.

Unlike other fungi, the lichens are not a single organism, but rather a symbiotic association between a fungus and an alga. The fungal member of the lichen is usually an ascomycete basidiomycete, and the alga is usually a cyanobacterium or a chlorophyte (green alga). Often the fungal partner is unable to grow without the algal symbiont, making it difficult to classify these organisms. They will be treated here as a separate group, but it should be realized that they are neither single organisms, nor a monophyletic group.

It should also be noted that some organisms carry the name of mold or fungus, but are NOT classified in the Kingdom Fungi. These include the slime molds and water molds (Oomycota). The slime molds are now known to be a mixture of three or four unrelated groups, and the oomycetes are now classified in the Chromista, with the diatoms and brown algae.

In addition to being filamentous, fungal cells often have multiple nuclei. In the chytrids and zygomycetes, the cells are coenocytic, with no distinction between individual cells. Rather, the filaments are long and tubular, with a cytoplasm lining and large vacuole in the center. By contrast, the ascomycetes and basidiomycetes are septate; their filaments are partitioned by cellular cross-walls called septa. The structure of these septa varies, and is taxonomically useful.

Another feature of fungi is the presence of chitin in their cell walls. This is a long carbohydrate polymer that also occurs in the exoskeletons of insects, spiders, and other arthropods. The chitin adds rigidity and structural support to the thin cells of the fungus, and makes fresh mushrooms crisp.

Most members of the kingdom Fungi lack flagella; the structures are completely absent in all stages of their life cycle. The only exception are the chytrids, which produce flagellated gametes. The absence of flagella then, is a synapomorphy which unites all the remaining groups of fungi. This has had a tremendous impact on fungal biology, because it means that no fungus can produce motile gametes, and two organisms must therefore come into direct physical contact to effect sexual reproduction.

Fungi cause diseases

Fungi also cause a number of plant and animal diseases: in humans, ringworm, athlete's foot, and several more serious diseases are caused by fungi. Because fungi are more chemically and genetically similar to animals than other organisms, this makes fungal diseases very difficult to treat. Plant diseases caused by fungi include rusts, smuts, and leaf, root, and stem rots, and may cause severe damage to crops. However, a number of fungi, in particular the yeasts, are important "model organisms" for studying problems in genetics and molecular biology.

Fungi are fossils

While fungi are not uncommon fossils, their fossils have not received a great deal of attention compared to other groups of fossils. Their fossils tend to be microscopic; very few large fungal bodies, such as mushrooms, have ever been found as fossils. Fossil fungi are often difficult or impossible to identify. The fungal filaments shown above at left are a case in point; found in Cretaceous amber from north France, they resemble living filaments of the common ascomycete Candida; however, since there is little information on how this fossil organism lived or how it reproduced (both important in recognizing modern taxa), its true affinities may never be known. By contrast, the Miocene fossil at right above has preserved the perithecium, an enclosed reproductive structure. Features of the spores and the perithecium in which they occur suggest that this may be a fossil species of Savoryella.

Recent careful studies of some well-preserved material have contributed much to our knowledge of fossil fungi. In particular, microscopic examination of fossil fungi from the Devonian-age Rhynie Chert in Aberdeenshire, Scotland, has shown that fungi and land plants were forming symbiotic relationships even at that very early stage in terrestrial evolution. In fact, all four major groups of modern fungi have now been found in Devonian strata, showing that the fungi had successfully invaded the land and begun to diversify before the first vertebrates crawled out of the sea!

Symbiotic relationship between fungi and plants.

Most plants rely on a symbiotic fungus to aid them in acquiring water and nutrients from the soil. The specialized roots which the plants grow and the fungus which inhabits them are together known as mycorrhizae, or "fungal roots". The fungus, with its large surface area, is able to soak up water and nutrients over a large area and provide them to the plant. In return, the plant provides energy-rich sugars manufactured through photosynthesis. Examples of mycorrhizal fungi include truffles and Auricularia, the mushroom which flavors sweet-and-sour soup.

In some cases, such as the vanilla orchid and many other orchids, the young plant cannot establish itself at all without the aid of its fungal partner. In liverworts, mosses, lycophytes, ferns, conifers, and flowering plants, fungi form a symbiotic relationship with the plant. Because mycorrhizal associations are found in so many plants, it is thought that they may have been an essential element in the transition of plants onto the land.

Sexual phase of fungi

The sexual phase is begun when haploid hyphae from two different fungal organisms meet and fuse. When this occurs, the cytoplasm from the two cells fuses, but the nuclei remain separate and distinct. The single hypha produced by fusion typically has two nuclei per "cell", and is known as a dikaryon, meaning "two nuclei". The dikaryon may live and grow for years, and some are thought to be many centuries old. Eventually, the dikaryon forms sexual sporangia in which the nuclei fuse into one, which then undergoes meiosis to form haploid spores, and the cycle is repeated.

Some fungi, especially the chytrids and zygomycetes, have a life cycle more like that found in many protists. The organism is haploid, and has no diploid phase, except for the sexual sporangium. A number of fungi have lost the capacity for sexual reproduction, and reproduce by asexual spores or by vegetative growth only. These fungi are referred to as Fungi Imperfecti, and include, among other members, the athlete's foot and the fungus in bleu cheese. Other fungi, such as the yeasts, primarily reproduce through asexual fission, or by fragmentation -- breaking apart, with each of the pieces growing into a new organism.

Fungi are heterotrophic

Fungi are not able to ingest their food like animals do, nor can they manufacture their own food the way plants do. Instead, fungi feed by absorption of nutrients from the environment around them. They accomplish this by growing through and within the substrate on which they are feeding. Numerous hyphae network through the wood, cheese, soil, or flesh from which they are growing. The hyphae secrete digestive enzymes which break down the substrate, making it easier for the fungus to absorb the nutrients which the substrate contains.

This filamentous growth means that the fungus is in intimate contact with its surroundings; it has a very large surface area compared to its volume. While this makes diffusion of nutrients into the hyphae easier, it also makes the fungus susceptible to dessication and ion imbalance. But usually this is not a problem, since the fungus is growing within a moist substrate.

Most fungi are saprophytes, feeding on dead or decaying material. This helps to remove leaf litter and other debris that would otherwise accumulate on the ground. Nutrients absorbed by the fungus then become available for other organisms which may eat fungi. A very few fungi actively capture prey, such as Arthrobotrys which snares nematodes on which it feeds. Many fungi are parastitic, feeding on living organisms without killing them. Ergot, corn smut, Dutch elm disease, and ringworm are all diseases caused by parasitic fungi.

Biodiversity, Conservation and Utilization Of Fungi

Biodiversity of fungi is any important aspect to be dealt with utmost scientific accuracy and accountability. One third of fungal diversity of the globe exists in India. Out of 1.5 million of fungi, only 50% need to be identified. Unfortunately around 5-10% of fungi are cultured artificially. The variety and galaxy of fungi and their natural beauty occupy prime place in the biological worked and India has been the cradle for such fungi. Only a fraction of total fungal wealth has been subjected for scientific scrutiny and mycologists have to explore the unexplored and hidden wealth.

What is Biodiversity?

Biodiversity means the variability among living organisms from all sources including inter alia, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part. The term biodiversity embraces genetic diversity, species diversity, ecosystem diversity and agro biodiversity. 5-50 millions species of living form exists on the globe and of which 1.5 million are fungi. The vast numbers of fungi that are recorded exceed 72,036 (Hawksworth, 1991, 1997).

Fungal Diversity

The number of fungi recorded in India exceed 27,000 species, the largest biotic community recorded after insects (Sarbhoy et al 1996). The true fungi belongs of kingdom Eukaryota which has 4 phyla, 103 orders, 484 families and 4, 979 genera. The 4 phyla accepted in the seventh edition (Hawksworth et al 1995) are Ascomycota, Basidiomycota, Chytridiomycota and Zygomycota.

In the eighth edition of Dictionary of the fungi Hawksworth et al (1995) have recognized eleven phyla, the Deuteromycotina is not accepted as formal taxomic category. The number of fungal genera reported from world and form India are shown in the Table.

 
Phyla World India
Myxomycotina 450 380
Mastigomycotine 308 205
Zygomycotina 55 50
Ascomycotina 2000 745
Basidiomycotina 357 232
Deutecomycotina 4100 468
Total 7270 2080

The beauty and endless variety of fungi never cease to enchant biologists all over the globe. India has always been a strong centre and cradle for fungi. The fungal diversity that we saw the mycologists have unravelled through conventional techniques is only a fraction of the amazing real diversity. In order to explore the unexplored and un-explorable, the fungal specialists have to look up for newer tools, innovation, creation of novel media, selective enrichment techniques besides taking into account various ecological parameters.

MASTIGOMYCOTINA Fungi belonging to mastigomycotina forms the prevalent group of fungi in water. It comprises members of Chytridiomycetes, Hyphochytridiomyctes and Oomycetes. These fungi are known to colonize diversified habitats, which includes water, humid soils, insects, keratin, chitin, angiosperms, pollen grains and other by living either as saprophytes or parasites.

ZYGOMYCOTINA It is an assemblage of fungi, which reproduce asexually by sporangiospores, which are dispersed either violently, or passively by wind, rain or animals. Fungi or this subdivision are ubiquitous in soil and dung, occurring mostly as saprophytes although few are parasitic on plants and animals.

ASCOMYCOTINA Ascomyceteous fungi comprises of a wide variety of fungi differing in their morphology, ontogeny, ascocarp details, ascus organization, nature of ascospores, their ultra structure and other parameters besides occurring on diversified habitats. Yeasts are common in moist, sugar rich environment like plant surfaces and fruits but are also prevalent in soil, fresh and marine water bodies.

BASIDIOMYCOTINA Largely fleshy fungi which includes toadstools, bracket fungi, fairy clubs, puff balls stinkhorns, earthstars, bird nest fungi and Jelly fungi are the members of this group. These fungi live as saprophytes and some are serious agents of wood decay. Some toad stools, which are associated with trees form mycorrhiza, a symbiotic association (Harley, 1969) but some are severe parasites eg: Armillaria mellea which destroy a wide range of woody and herbaceous plants.

DEUTEROMYCOTINA The Deuteromycetes constitute an artificial group and are asexual phases of Ascomycotina and Basidiomycotina. The multiplication occurs by the production of mitotic spores or conidia from specialized hyphae call conidiophores.

MYCORRHIZA Some Fungi form symbiotic association with roots of plants, referred mycorrhizas are the most common among forest and ornamental tree species of the families prinaceae, Fagaceae, Salicaceae, Tiliaceae besides forming mycorrhiza in Casuarina and Eucalyptus.

ARBUSCULARMYCORRHIZAL FUNGI In many agricultural, horticultural, medicinal, fiber, ornamental, mostly shrubs and tropical tree species AM fungi form obligate symbiotic association, in addition to their widespread distribution in phosphorous and other nutrient deficient soils. These fungi colonize around 80% of plants existing on the globe.

ANAMORPHS, TELEOMORPHS AND HOLOMORPHS Taxonomy is the mother of all sciences Identification criteria should be accurate and scientific. It should be devoid of misdeterminations and misapplication of names. Confusion in the terminology should not exist. Anamorph is nothing but an asexual stage (mitospora) and the Teleomroph denotes perfect stage (Meiotic diaspore).

CONIDIAL FUNGI IN WATER Water is an important resource and harbors a variety of biotic communities belonging to plant and animal kingdom. Among the fungi conidial fungi are found in aerobic water bodies being frequently distributed on foam and on submerged leaves. In total 60 conidial fungi are reported from Indian sub-continent.

Ideas for using fungi for Science Projects

Do different wild-type strains of Neurospora differ in the timing of pigmentation if you grow them in the dark then move them to the light?
Do biochemical mutants have different abilities to grow on natural substrates (eg fruits, vegetables, bread, paper, cloth)?
Do different strains of the same fungus differ in their ability to grow on natural substrates ?
Do different wild strains of Neurospora produce different numbers of conidia?
Do conidia from different strains differ in their ability to survive environmental stresses like heating, freezing, or dessication?
Do different strains differ in their ability to tolerate toxins?
Are common environmental toxins toxic to Neurospora or Aspergillus?
Do common cleansers kill fungal spores?
Can common products produce mutations?
Can common products disrupt sexual reproduction?
How do different fungi compete if they are mixed in culture?
Can different fungi out-compete one another depending on the growth medium or natural substrate?
Can common fungi be isolated from our surroundings?
What kinds of fungi are found in soil, air, produce, or water?
Do fungi of different colors produce useful dyes?

Communities Of Fungi and Ecology

Fungi are known to play vital roles as decomposers, symbionts of plants and animals and are also parasites on plants in different ecosystems. Out of 1.5 million species of fungi, are many may remain un-described. Fungi interact with their hosts, substrates, and also with abiotic variables of their environment. Fungi grow in every conceivable habitat/substrate having organic carbon. They can occur in extreme habitats experiencing high and low temperature, on dry substrates and in concentrated nutrients.

Pollen grains, insect parts, fungal spores, bacteria, vegetable debris and dust particles are carried by air. Fungal spores and pollen grains with allergenic properties pose a serious health hazard. Studies on the myco-organic content of air over crop fields have been useful in understanding the dissemination of air-borne pathogens and in establishing the forecasting system of disease control.

A number of fungi are found to colonize. Keratin substrates like human hair, nails etc. The fungal members belonging to Microsporum, Trichophyton and Epicermophyton are common and potential disease causing agents.

Fungal Conservation

Threats to fungi throughout the globe lead to their extinction and such acts have prompted debates about whether the fungi can be conserved. It involves the conservation of site, substrate or the habitat, host and artificial culturing of fungi and their maintenance. Fungi are not only beautiful but also play significant role in human welfare. Conservation is a major concern at the moment. In the last 40 years mycologists became aware of a general decline in natural habitats resulting in the dwindling of a number of genera and species in their occurrence.

All the nations have decided at Rio de Janeiro in 1992 conference (UNCED) that the global biodiversity must be conserved immediately since many fungi, plants, animals and other have become extinct during 20th century and several others are at the verge of extinction due to their over exploitation, degradation of the habitats and other reasons.

Utilization Of Fungi and Fungal Biotechnology

Role of fungi is well established in fermentation technology and using this industrial processes, many metabolites are commercially exploited for their antibiotic properties. Cephalosporin, penicillin and griseofulvin are derived from fungi. Yeast forms an important agent in fermentation to produce ethanol from sugar or after hydrolysis from starch and cellulose.

Plant diseases such as blights, wilts, rust smuts, cankers, leaf spots, blast etc on a number crop plants and forest plants have become important as they dwindle country's economy. Bio deterioration is a biological process that contributes to deterioration or destruction of material resulting in economic loss. Biodegradation refers to the biological breakdown of undesirable materials or compounds to harmless or tolerable products. Application of mycoherbicides to control weeds has been an age-old approach through classical methods in which plant pathogens are released to control of weeds through natural spread.

Commercialized Fungal Products

Biotechnology is the application of living organisms and their component to industrial products and processes is not an industry in itself, but an important technology that will have large impact on many different industrial sectors in future. Traditional products include bread, beer, cheese and wine. In textile and enzymatic removal of starch size from woven fabrics has been in use for most of this century and the fermentation vat is probably the oldest known dyeing process. Today pure strains of yeast are normally employed and 1.5 million tons of baker's yeast is produced worldwide every year. Cultivation of edible mushroom outdoors has been practiced for hundreds if not thousands of years.

Many more fungi, which are hidden underneath, the ecological niches to be surveyed, cultured, studied, classified, conserved and utilized for human welfare. Fungi are cosmopolitan, ubiquitous, beautiful, economically useful, used for human welfare, micro-macroscopic and are the natural scavengers, hence deserve promotion. Out dedicated approach is essential in studying them, classifying them, growing and multiplying them.

 

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