The extracytoplasmic function σ factor σC regulates expression of a branched quinol oxidation pathway in Corynebacterium glutamicum

Bacteria modify their expression of different terminal oxidases in response to oxygen availability. Corynebacterium glutamicum, a facultative anaerobic bacterium of the phylum Actinobacteria, possesses aa(3)-type cytochrome c oxidase and cytochrome bd-type quinol oxidase, the latter of which is induced by oxygen limitation. We report that an extracytoplasmic function sigma factor, sigma(C), is responsible for the regulation of this process. Chromatin immunoprecipitation with microarray analysis detected eight sigma(C)-binding regions in the genome, facilitating the identification of a consensus promoter sequence for sigma(C) recognition. The promoter sequences were found upstream of genes for cytochrome bd, heme a synthesis enzymes and uncharacterized membrane proteins, all of which were upregulated by sigC overexpression. However, one consensus promoter sequence found on the antisense strand upstream of an operon encoding the cytochrome bc(1) complex conferred a sigma(C)-dependent negative effect on expression of the operon. The sigma(C) regulon was induced by cytochrome aa(3) deficiency without modifying sigC expression, but not by bc(1) complex deficiency. These findings suggest that sigma(C) is activated in response to impaired electron transfer via cytochrome aa(3) and not directly to a shift in oxygen levels. Our results reveal a new paradigm for transcriptional regulation of the aerobic respiratory system in bacteria.