Oxygen Regulation of the ccoN Gene Encoding a Component of the cbb(3) Oxidase in Rhodobacter sphaeroides 2.4.1(T): Involvement of the FnrL Protein

The ccoNOQP gene cluster of Rhodobacter sphaeroides 2.4.1(T) encodes a cbb(3) cytochrome oxidase which is utilized in oxygen-limited conditions for aerobic respiration. The β-galactosidase activity of a ccoN::lacZ transcriptional fusion was low under high (30%)-oxygen and anaerobic growth conditions. Maximal ccoN::lacZ expression was observed when the oxygen concentration was lowered to 2%. In an FnrL mutant, ccoN::lacZ expression was significantly lower than in the wild-type strain, suggesting that FnrL is a positive regulator of genes encoding the cbb(3) oxidase.