Identification and characterization of the genes encoding carbon monoxide dehydrogenase in Terrabacter...

Terrabacter carboxydivorans is able to grow aerobically at low concentrations of carbon monoxide (CO) as a sole source of carbon and energy. The genes for carbon monoxide dehydrogenase (CO-DH) were cloned from T. carboxydivorans and analyzed. The operon encoding T. carboxydivorans CO-DH was composed of three structural genes with the transcriptional order of cutB, cutC and cutA, as well as an additional accessory gene (orf4). Phylogenetic analysis of CutA revealed that T. carboxydivorans CO-DH was classified into a group distinct from previously characterized CO-DHs. Expression of antisense RNA for the cutB or cutA gene in T. carboxydivorans led to a decrease in CO-DH activity, confirming that cutBCA genes are the functional genes encoding CO-DH. The CO-DH operon was expressed even in the absence of CO and further inducible by CO. In addition, CO-DH synthesis was increased in the stationary phase compared to the exponential phase during heterotrophic growth on glucose and glycerol. Point mutations of a partially inverted repeat sequence (TCGGA-N₆-GCCCA) in the upstream region of the cutB gene almost abolished expression of the CO-DH operon, indicating that the inverted-repeat sequence might be a cis-acting regulatory site for the positive regulation of the CO-DH operon.