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Cooperation

	Cooperation Cooperation in a single colony of microorganisms is evidenced by extended lag period. For example, when a very small inoculum is used for culture, failure of growth results since there is an extended lag phase or a complete absence of growth. This is true for fastidious organisms and is a major obstacle to isolation procedures. Population of intermediate density are more successful than individual organisms for colonisation of natural habitats. Minimum infectious dose of pathogen or a single pathogen (a single cell) fails to cause disease.
How does cooperation occur? The semi-permeable membranes of microorganisms are imperfect and tend to leak low molecular weight metabolic products that are essential for biosynthesis and growth. Hence, within a Population there are more concentrations of these extracellular metabolites that counteract the loss and facilitate re-absorption. But in a single cell or at very low population densities, loss exceeds replacement rates and prevents growth. A large population can adjust to an initially unfavourable culture medium but a very small population may be unable to do so.
The basis of cooperation is colony formation. Motile bacteria that tend to move away often remain in colonies. Association of a population within a colony allows for more efficient utilisation of available resources and to seek new sources of nutrients (mass movement of colony). For example, in the slime mold, Dictyostelium, when the food resources become limited, the usually amoeboid colonies swarm together to form a central organism through the release of cyclic AMP. The cells unite to form a fruiting body which forms spores that disseminate and germinate to form the amoeboid colony. Thus during unfavourable conditions, the cells form a colony and tide over the condition. This is a fine example of microbial cooperation

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