Dimorphism and other forms of fungi

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Majority of fungal organisms cause disease in plants, animals and humans but many fungi serve beneficial purposes to mankind and his environment. Fungi are used in a number of industrial processes that involves fermentation. Some notable antibiotics (for example, penicillin), foods (for example, bread and cheese) and drinks (for example, alcoholic and non-alcoholic beverages) are typical products of the fermentative action or activities of fungi and other microbes. Some fungi can exist as both yeast (especially in the parasitic phase) and moulds (especially in the saprophytic phase) in different conditions; and such fungi are generally known as dimorphic or diphasic fungi. Dimorphism is the phenomenon or condition in which a particular fungus exists in two morphological or growth forms viz: yeast and mould forms. It is an important pathogenicity mechanism employed by a number of fungal pathogens, especially those that are responsible for causing systemic and opportunistic mycoses in humans. These fungal pathogens that exhibit dimorphism include but not limited to Candida albicans, Histoplasma capsulatum, Paracoccidioides brasiliensis, Blastomyces dermatitidis, Sporothrix schenckii, and Penicillium marneffei. Other forms of fungi include mushrooms, puffballs and mildews. Mushroom as aforementioned, is another group or class of fungi but they are macro-fungal cells that possess many economic and health benefits to humans.

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Mushrooms are the macroscopic reproductive or fruiting bodies of fungi. They are visible and can be seen around our homes, in bushes, on stored or baked foods and in farms. Mushroom farming is big time business in many parts of the world, and some mushrooms (for example, Agaricus bisporus) are important source of food for humans. Other edible mushrooms include Lentinula species, Pleurotus species, Volvariella species and Ganoderma species. Mushrooms possess medicinal value aside their edible and nutritional benefits. Generally, mushrooms are important source of proteins, low fats, vitamins, carbohydrates, minerals and fibers for humans. Slime moulds were formerly classified as a form of fungi because they exhibit some fungal characteristics (especially the formation of fruiting bodies) but this is no longer the case as the organism is more protists-like than fungi. Slime moulds are motile amoebic organisms and they differ from fungi phylogenetically even though they may resemble fungal organisms in some way. Unlike bacteria and some prokaryotes that have a peptidoglycan cell wall, fungi have a chitinized rigid cell wall (i.e., cell wall that contains chitin).

Fungal cell wall also contains cellulose, lipids, polysaccharides and other complex organic molecules. Fungi are much larger than prokaryotic cells (bacteria in particular), and their cell membrane is very rich in sterols (for example, ergosterol). Cholesterol and not ergosterol is the sterol that makes up the cell membrane of mammalian and human cells. Most fungal drugs (for example, amphotericin B) are selectively toxic because they target the ergosterol component of the fungal cell membrane since the mammalian cell membrane is mainly made up of cholesterol. Fungi produce sexual and asexual spores that help in their dispersal and reproduction in the natural environment. In bacteria, spore production or formation is strictly for survival purposes especially when environmental condition is harsh for existence but spores of fungi are used for reproduction and dispersal purposes. Fungi cause a variety of infections in human population as well as in plants and animals.

Further reading

Anaissie E.J, McGinnis M.R, Pfaller M.A (2009). Clinical Mycology. 2nd ed. Philadelphia, PA: Churchill Livingstone Elsevier. London.

Baumgardner D.J (2012). Soil-related bacterial and fungal infections. J Am Board Fam Med, 25:734-744.

Calderone R.A and Cihlar R.L (eds). Fungal Pathogenesis: Principles and Clinical Applications. New York: Marcel Dekker; 2002.

Champoux J.J, Neidhardt F.C, Drew W.L and Plorde J.J (2004). Sherris Medical Microbiology: An Introduction to Infectious Diseases. 4th edition. McGraw Hill Companies Inc, USA.       

Dix, N.J.  and Webster, J.  (1995). Fungal Ecology. Chapman and Hall, London.

Gladwin M and Trattler B (2006). Clinical Microbiology Made Ridiculously Simple. 3rd edition. MedMaster, Inc., Miami, USA.

Larone D.H (2011). Medically Important Fungi: A Guide to Identification. Fifth edition. American Society of Microbiology Press, USA.

Madigan M.T., Martinko J.M., Dunlap P.V and Clark D.P (2009). Brock Biology of Microorganisms, 12th edition. Pearson Benjamin Cummings Inc, USA.

Stephenson S.L (2010). The Kingdom Fungi: The Biology of Mushrooms, Molds and Lichens. First edition. Timber Press.

Sullivan D.J and Moran G.P (2014). Human Pathogenic Fungi: Molecular Biology and Pathogenic Mechanisms. Second edition. American Society of Microbiology Press, USA.

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