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Index >> Population Interactions >> Commensalism

Commensalism

	Commensalism Mensa in Latin means table which further denotes' one organism lives off the table scraps of another one'. Commensalism is a unilateral relationship and it results when the unaffected population modifies the habitat so that another population benefits. The modification of the environment by the facultative anaerobes for the obligate ones is an excellent example for this.
Commensalism is exhibited in a number of ways as listed below. 1. When there is a need for the production of growth factors commensalism plays an important role. For example, Flavobacterium brevis excretes cysteine which is taken up by Legionella pneumophila. 2. Transformation of insoluble compounds to soluble ones and further into gaseous components is observed in commensalism. For example, methane from sediment benefits methane oxidising population in the overlying water and hydrogen sulphide production in buried sediments which helps the photo-autotrophic sulphur bacteria on the sediment surface.
3. Conversion of organic molecules by one population which become substrates for other population is also commonly seen. For example, fungi release extracellular enzyme which decomposes lignin to form simple glucose moieties which benefit the other microorganisms. 4. Two organisms tend to remain together to satisfy their metabolic needs. For example, Mycobacterium vaccae, growing on propane as a source of carbon and energy, will gratuitiously oxidise cyclohexane to cyclohexanone which is readily used up by other microorganisms like Pseudomonas. Here Pseudomonas benefit because they are unable to metabolise cyclohexane, whereas the Mycobacterium remains unaffected because it does not assimilate cyclohexanone.
5. Removal or neutralisation of a toxic material is also observed. For example, oxidation of hydrogen sulphide by Beggiatoa detoxifies it, thus benefiting the H2S sensitive aerobic organisms. Some tend to detoxify through immobilisation. For example, Leptothrix reduces manganese concentration thus permitting the growth of other microbes to which higher manganese concentration would be toxic.

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