Contribution of the fnr and arcA gene products in coordinate regulation of cytochrome o and d oxidase (cyoABCDE and cydAB) genes in Escherichia coli.

The individual and the combined effect of the fnr and arcA regulatory gene products on cytochrome o oxidase and cytochrome d oxidase gene expression in Escherichia coli were evaluated using lacZ reporter fusions to the cyo-ABCDE and cydAB operons. Fnr repressed cyo-lacZ and cyd-lacZ expression during anaerobic growth but not during aerobic growth conditions. ArcA functioned as an anaerobic repressor of cyo-lacZ expression while, in contrast, it activated cydAB expression during both aerobic and anaerobic growth. ArcA and Fnr appear to function independently of each other to control cyo-ABCDE operon expression. In contrast, FNR repression of cydAB expression was dependent on arcA+, as indicated by the inability of fnr+ plasmids to repress cyd-lacZ expression in an arcA strain. Under no conditions tested did Fnr activate cydAB expression. Most, but not all, of the observed aerobic/anaerobic regulation of cyo and cyd was accounted for by the two transcriptional regulators. These data suggest the existence of additional levels of anaerobic gene control in E. coli. Additionally, the expression of the fnr regulatory gene, and regulation of the anaerobic respiratory genes, narGHJI, dmsABC and frdABCD, was found to be independent of ArcA.