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

The expression and transcriptional regulation of the Escherichia coli cyx-appA operon and the appY gene have been investigated under differe nt environmental conditions with single-copy transcriptional lacZ fusi ons. The cyx-appA operon encodes acid phosphatase and a putative cytoc hrome oxidase. ArcA and AppY activated transcription of the cyx-appA o peron during entry into stationary phase and under anaerobic growth co nditions. The expression of the cyx-appA operon was affected by the an aerobic energy metabolism. The presence of the electron accepters nitr ate and fumarate repressed the expression of the cyx-appA operon. The nitrate repression was partially dependent on NarL. A high level of ex pression of the operon was obtained in glucose medium supplemented wit h formate, in which E. coli obtains energy by fermentation, The format e induction was independent of the fhlA gene product. The results pres ented in this paper indicate a clear difference in the regulation of t he 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 a naerobiosis, and this anaerobic induction is independent of Fnr, and A ppY, but dependent on ArcA. The expression of the appY gene is not aff ected significantly by the anaerobic energy metabolism, i.e., fermenta tion 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 inverse ly correlated with the growth rate and is induced by phosphate starvat ion as well as during entry into stationary phase. During oxygen-limit ing conditions the stationary-phase induction is partially dependent o n 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.