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The addition of exogenous pyrophosphate increases the growth yield and cAMP synthesis in stationary phase when Escherichia coli is grown in minimal medium. Pyrophosphate increases the yield by altering the enterobactin uptake system. We studied the physiological effects and examined how the E. coli transcriptome was modified when two structural analogs of pyrophosphate were added to the growth medium. Methylenediphosphonic acid or a high concentration of iron had the same positive effects as pyrophosphate on growth yield, cAMP synthesis and the repression of Fur-regulated genes. In contrast, imidodiphosphate did not affect these cellular processes significantly. The transcriptome modifications generated by pyrophosphate or methylenediphosphonic acid were more similar than those generated by imidodiphosphate or excess iron. The transcriptome data also indicated that processes other than iron uptake might be involved in the cellular response to exogenous pyrophosphate or methylenediphosphonic acid., (Copyright 2003 S. Karger AG, Basel)

Microbial catabolism of phenylpropanoid compounds plays a key role in the degradation of aromatic molecules originating from the degradation of proteins and plant constituents. In this study, the regulation of the early steps in the utilisation of 3-phenylpropionate, a phenylpropanoid compound, was investigated. Expression of the hcaA gene product, which is involved in 3-phenylpropionate catabolism in Escherichia coli, was positively regulated by HcaR, a regulatory protein similar to members of the LysR regulators family. Remarkably, the expression of hcaA in the presence of 3-phenylpropionate was sharply and transiently induced at the end of the exponential growth phase. This occurred in a rpoS-independent manner. This transient induction was also mediated by HcaR. The expression of this positive regulator is negatively autoregulated, as for other members of the LysR family. The expression of hcaR is strongly repressed in the presence of glucose. Glucose-dependent repression of hcaR expression could only be partially overcome by adding exogenous cAMP.