Escherichia coli habitats, cell types, and molecular mechanisms of gene control.

Escherichia coli cycles between 2 principal habitats-intestines of warm-blooded animals and water, sediment and soil-that are distinct with respect to physical conditions and the spectrum and level of available nutrients. On average, an E. coli cell is 'born' in the intestine of a warm-blooded animal and spends about half its life there, is excreted onto the surface of the earth where it spends the 2nd half of its life, and then dies or, with a small probability, colonizes a new host. One can predict that E. coli will have at least 2 phenotypically distinct cell types and that these will have dual molecular control mechanisms of opposite type for the regulation of certain functions. In cases for which the molecular data are available for comparison, they agree with predictions. -from Author