Physiological function and regulation of flavocytochrome c3, the soluble fumarate reductase from Shewanella putrefaciens NCIMB 400

Shewanella putrefaciens produces a soluble flavocytochrome c under anaerobic growth conditions. This protein shares sequence similarity with the catalytic subunits of membrane-bound fumarate reductases from Escherichia coli and other bacteria and the purified protein has fumarate reductase activity. It is shown here that this enzyme, flavocytochrome c(3), is essential for fumarate respiration in vivo since disruption of the chromosomal fccA gene, which encodes flavocytochrome c(3), leads to a specific loss of the ability to grow with fumarate as terminal electron acceptor. Growth with nitrate, trimethylamine N-oxide (TMAO) and other accepters was unaffected. The fccA gene is transcribed as a 2 kb monocistronic mRNA. An adjacent reading frame that bears limited sequence similarity to one of the membrane anchor subunits of E. coli fumarate reductase is not co-transcribed with fccA. Expression of the fccA gene is regulated by anaerobiosis and by the availability of alternative electron accepters, particularly nitrate and TMAO. DNA sequences have been identified that are required for this regulation.