Amensalism

Amensalism

	Amensalism In amensalism, one microbial population growing on a substrate is inhibitory to the other population. This relationship is based on the production of certain microbicidal chemicals (allelopathic substances) or antibiotics. Amensalism leads to pre-emptive colonisation of a habitat, i.e. once an organism establishes itself within a habitat, it prevents other population from surviving in that habitat. For example, lactic acid bacteria prevent other microbial population from surviving in its substrate by producing large amounts of acids that prove detrimental to the other microbial population. Similarly, E.coli cannot survive in the rumen due to the production of volatile fatty acids produced by the already existing anaerobes.
Fatty acids produced by microbes on the skin surface prevent the colonisation of these surfaces by other organisms like yeasts. Similarly, acids produced by microorganisms in the vaginal tract are responsible for preventing infection by Candida albicans. Some other examples of amensalism are: oxidation of sulphur by Thiobacillus thiooxidans which produces sulphuric acid which lowers aquatic pH thereby inhibiting many other microbes. Production of oxygen by algae may alter the habitat that can prove detrimental to obligate anaerobes. Zymogenous populations grow under condition of high organic matter which permit the production of antibiotics. For example, Cephalosporium graminerum is a wheat pathogen that grows in dead wheat tissue and produces antifungal antibiotics to prevent attack by other fungi.
Similarly Trichophyton mentagrophytes (a dermatophytic fungi) in the skin of New Zealand hedgehog produces penicillin (an antibiotic) on the skin and prevents the growth of the penicillin sensitive Staphylococcus aureus which is otherwise a common inhabitant of the skin. Bacteriocins are similar to antibiotics but their action is restricted to microorganisms very closely related to each other. They are peptides coded by plasmids and they are produced by one population to inhibit other microbial populations. For example, Lactobacillus species produce NISIN a bacteriocin that preserves food material like dairy products from spoilage by other bacteria

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