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| Fig. 1 - Mucor |
From
the microscopic yeasts to the largest mushrooms, many fungi have proved to be
beneficial to both humans and the environment.
Members of
the fungal kingdom, present in the soil, air, water and other living organisms,
represent a wide range of species. Many are harmful, causing damage to crops
and diseases in humans and animals. A large number of fungi, however, are of
immense use, both to humans and to the environment in general.
Fungi as Decomposers
Many fungi
play an important role in decomposing organic matter, and are thus instrumental
in the cycling of minerals. In natural systems, for instance, species of
Trichoderma, Phanerochaeta, Penicillium, Fusarium and Agaricus contain enzymes
capable of digesting both the lignin and cellulose in dead forest trees and
leaf litter. Valuable carbon, nitrogen and phosphorous are subsequently
returned to the soil.
Some
species of Rhizopus and Aspergillus can in fact decompose chemical pollutants
such as aniline and benzene, while certain strains of Penicillium can degrade
plasticisers, insecticides and herbicides. Moreover, the ability of fungi such
as Cladosporium resinae to utilize hydrocarbons has been
investigated as a possible solution to oil spillage issues.
The
advantage of fungal, as opposed to bacterial, decomposition, is that most fungi
develop far -reaching threads, or ‘hyphae’, which can penetrate and digest a
larger area of organic waste than bacterial colonies. Examples include the
hyphae of Mucor species (see figure 1), which grow quickly under favourable
conditions, secreting hydrolytic enzymes as they spread over nutrient-rich
organic matter.
Drugs from Fungi
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| Fig. 2 - Coralorrhiza |
The fungus Tolypocladium
inflatum is a source of the immunosuppressant drug Cyclosporin, used
in bone marrow and organ transplants and instrumental in the treatment of
autoimmune diseases. Other medicinal fungi include Aspergillus and Phoma
species, which produce statins - drugs that assist in the reduction of
low-density blood lipoproteins.
In
addition, Claviceps pupurea, a fungus perhaps better known for the
deadly disease ergotism, is often used in the treatment of migraines and blood
pressure. Yeasts are also regularly used in genetic engineering procedures to
produce recombinant
vaccines such as the Hepatitis B Virus vaccine.
Fungi as Symbionts
The
ability of some fungi to form symbiotic associations with plants is of great
importance in ecosystems. Around eighty five per cent of plants acquire
nutrients from mycorrhizal fungi associated with their root systems. The fungi,
in turn, utilize some of the sugars produced by the plants in photosynthesis.
Members of the Basidiomycetes family, for instance, form mycorrhizal soil
associations with conifers.
Interestingly,
some orchids tap into mycorrhizal fungi growing at the base of other plants to
obtain their nutrients. An example of this phenomenon, known as
myco-heterotrophy, can be observed in the Pacific Coralroot orchid (see figure
2). Lichens are another intriguing instance of fungi living symbiotically with
plants. The plants in this case are members of the genus Trebouxia, a type of
green alga. Each organism in this association depends on the other for
survival.
Fungi and Food Production
The
unicellular fungus, Saccharomyces cerevisciae, commonly known as
yeast, has played a vital role in the manufacture of bread and alcohol for
thousands of years. As yeasts feed off sugars in anaerobic respiration, they
release carbon dioxide and ethanol. In bread making, the carbon dioxide
produced helps the dough to rise, while any ethanol released is destroyed in
the baking process.
When
yeasts are used to produce wine, the carbon dioxide is either allowed to escape
or retained to form sparkling beverages. The inability of yeasts to survive in
high amounts of ethanol limits wine alcohol concentrations to around 15%. In
beer making, brewer’s yeast ferments the sugars produced by germinated cereal
grains such as barley, and the resulting ethanol is combined with hops to form
the final product.
Other
fungi involved in food production include Penicillium species, used in blue
cheeses, Aspergillus oryzae, which grows on rice to produce
soy sauce and the Japanese dish, koji, and Mucorales varieties, used to produce
the food additive beta-carotene. Rhizopus oligosporus, a type of
bread mould, is used to make the Indonesian dish, Tempeh, by fermenting
leguminous seeds. Macroscopic fungi such as shiitake, agaricus and enoki
mushrooms and truffles have
also been cultivated and eaten for hundreds of years.
Biological Control
Some
species of fungi have been introduced to agricultural crops as a form of
biological control of insect pests. Many of these belong to the Hyphomycetes
family, and target a range of insects, including thrips, caterpillars, aphids
and mealy bugs.
Fungi,
then, are an integral part of our natural and man-made surroundings. By
contributing to the cycling of minerals, waste decomposition, food production
and human medicine, they have consistently proved themselves to be an
indispensable kingdom.
References
•
C.S.I.R.O., Australia, 2003, 'What do Fungi do?', fungibank.csiro.au
•
Fungi as Food Sources, singnet.com
•
Fungi as Saprobes, blue.com
•
Teh, J.S., 1973, ‘Utilisation of n-alkanes by Cladosporium resinae’,
mendeley.com
•
University of Sydney, 2004, ‘Drugs From Fungi’, usyd.edu.au
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