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Many species of bacteria live in environments where nutrients are in short supply. Individual species must therefore accumulate nutrients at rates commensurate with rapid growth and successful competition. In order to increase the uptake of a given nutrient metabolic energy is used in its transport across the cell membrane (Button, 1985). In Escherichia coli, the ubiquitous model microorganism, transport processes are energised by several mechanisms (Fig.l). Energy sources used include: trans-membrane electrochemical gradient, of protons or sodium; adenosine triphosphate (ATP); or phosphoenol pyruvate (PEP) (illustrated in Fig.l; reviewed in Button, 1985; Saier, 1985; Henderson, 1986). |
