Escherichia coli Habitats, Cell Types, and Molecular Mechanisms of Gene Control

Escherichia coli cycles between two principal habitats-intestines of warm-blooded animals and water, sediment, and soil-that are shown to be quite distinct with respect to physical conditions and the spectrum and level of available nutrients. Elementary calculations suggest that, on the 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 second half of its life, and then dies or, with a small probability, colonizes a new host. From this information one can predict that E. coli will have at least two 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 are in agreement with the predictions.