ABSTRACT
Cultures of a single microorganism may occur naturally only in circumstances where extreme selection pressure operates. Generally, however, many different organisms with diverse metabolic potential will exist side by side. Therefore, metabolic interactions are probably the rule rather than the exception in natural ecosystems and biological treatment systems. Both the nature and the tightness of the association may vary widely, and the degradation of a single compound may necessitate the cooperation of two (or more) organisms. Some well-defi ned interactions and the different mechanisms underlying the cooperation are illustrated by the following examples:
1. One of the organisms fulfi lls the need for a growth requirement by the other, for example, vitamin requirements of one organism that is provided by the other. Examples are provided by biotin in cocultures of Methylocystis sp. and Xanthobacter sp. (Lidstrom-O’Connor et al. 1983), and thiamin in cocultures of Pseudomonas aeruginosa and an undefi ned Pseudomonas sp. that degraded the phosphonate herbicide glyphosate (Moore et al. 1983).
