In some cases, one species alone cannot degrade a toxic chemical and may require the cooperation of more than one or more additional species. This is called synergism. Several mechanisms for synergism are proposed. (1) One or more species provide growth factors such as B vitamins and amino acids. (2) One species grows on the toxic chemical and causes incomplete degradation yielding one or several intermediate products, and the second species then completely degrades the products formed due to incomplete degradation by the first bacterium. In the absence of second bacterium, these products tend to accumulate in the environment. (3) The first species cometamobolizes the toxic chemical to yield a product it cannot degrade and the second species then metabolizes this product. In this instance, the first species does not use the chemical as a carbon source. (4) The first species converts the substrate into a toxic product and only proceeds rapidly in the presence of second species. Presence of second species destroys the toxic compound. If second species is not present, the transformation either slows down or stops.
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