Effect of growth conditions on expression of the acid phosphatase (cyx-appA) operon and the appY gene, which encodes a transcriptional activator of Escherichia coli

Abstract

The expression and transcriptional regulation of the Escherichia coli cyx-appA operon and the appY gene have been investigated under different environmental conditions with single-copy transcriptional lacZ fusions. The cyx-appA operon encodes acid phosphatase and a putative cytochrome oxidase. ArcA and AppY activated transcription of the cyx-appA operon during entry into stationary phase and under anaerobic growth conditions. The expression of the cyx-appA operon was affected by the anaerobic energy metabolism. The presence of the electron acceptors nitrate and fumarate repressed the expression of the cyx-appA operon. The nitrate repression was partially dependent on NarL. A high level of expression of the operon was obtained in glucose medium supplemented with formate, in which E. coli obtains energy by fermentation. The formate induction was independent of the fhlA gene product. The results presented in this paper indicate a clear difference in the regulation of the cyx-appA operon and that of the cyd operon, encoding the cytochrome d oxidase complex. The results suggest that cytochrome x oxidase has a function under even more-oxygen-limiting conditions than cytochrome d oxidase. The expression of the appY gene is induced immediately by anaerobiosis, and this anaerobic induction is independent of Fnr, and AppY, but dependent on ArcA. The expression of the appY gene is not affected significantly by the anaerobic energy metabolism, i.e., fermentation versus anaerobic respiration. A model incorporating the anaerobic regulation of the appY gene and the two operons which are controlled by AppY, the hydrogenase 1 (hya) operon and the acid phosphatase (cyx-appA) operon, is presented. The expression of the appY gene is inversely correlated with the growth rate and is induced by phosphate starvation as well as during entry into stationary phase. During oxygen-limiting conditions the stationary-phase induction is partially dependent on ArcA. The alternative sigma factor sigma S has limited influence on the transcription of the appY gene during entry into stationary phase and no effect on the induction by phosphate starvation.