Gene structure and expression profile of cytochrome bc nitric oxide reductase from Hydrogenobacter thermophilus TK-6.

The genes for a nitric oxidereductase-like cytochrome bc complex were cloned from a thermophilic, chemolithoautotrophic hydrogen-oxidizing bacterium, Hydrogenobacter thermophilusTK-6. The structural genesnorC and norB, which encode cytochrome c and cytochrome bsubunits of the complex respectively, are probably transcribed as a tricistronic operon with a following gene encoding a putative membrane protein. NorC has, unusually, two hydrophobic transmembrane spans in its N-terminus. Immunoblot analysis showed that expression of NorC was induced by nitrate, nitrite, or sodium nitropurusside, suggesting that the norCB gene product is a denitrification enzyme, nitric oxidereductase. The consensus sequencesfor the DNR/NnrR-type or the NorR/FhpR-type nitric oxide-sensing regulators of proteobacteriawere not found in the norC promoter region, but consensus −35 and −10 sequences were found in this region. These results indicate that strain TK-6 has a nitrogen oxide-sensing regulatory system that differs from...