In Escherichia coli, expression of certain genes and operons, including the fructose operon, is controlled by Cra, the pleiotropic catabolite repressor/activator protein formerly known as FruR. In this study we have demonstrated that cra mutant strains synthesize 10-fold less cAMP than isogenic wild-type strains, specifically when grown in fructose-containing minimal media. The glucose-specific IIA protein (IIAgIc) of the phosphotransferase system, which activates adenylate cyclase when phosphorylated, is largely dephosphorylated in cra but not wild-type strains growing under these conditions. Dephosphorylation of llAglC in cra strains apparently results from enhanced fructose operon transcription and fructose uptake. These conclusions were supported by showing that f ructose-grown cra strains possess 2-5-fold higher fructose-l-phosphate kinase activity than fructose-grown wild-type strains. Moreover, artificially increasing fructose operon expression in cells transporting fructose dramatically decreased the activity of adenylate cyclase. The results establish that Cra indirectly regulates the activity of adenylate cyclase by controlling the expression of the fructose operon in cells growing with fructose as the sole carbon source.

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Peculiar attributes revealed by sequencing the genome of Desulfovibrio vulgaris Hildenborough are analyzed, particularly in relation to the presence of a phosphotransferase system (PTS). The PTS is a typical bacterial carbohydrate transport system functioning via group translocation. Novel avenues for investigations are proposed emphasizing the metabolic diversity of D. vulgaris Hildenborough, especially the likely utilization of mannose-type sugars. Comparative analysis with PTS from other Gram-negative and Gram-positive bacteria indicates regulatory functions for the PTS of D. vulgaris Hildenborough, including catabolite repression and inducer exclusion. Chemotaxis towards PTS substrates is considered. Evidence suggests that this organism may not be a strict anaerobic sulfate reducer typical of the ocean, but a versatile organism capable of bidirectional transmigration and adaptation to both water and terrestrial environments.