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

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Bacteria modify their expression of different terminal oxidases in response to oxygen availability.Corynebacterium glutamicum, a facultative anaerobic bacterium of the phylum Actinobacteria, possessesaa3-type cytochromecoxidase and cytochromebd-type quinol oxidase, the latter of which is induced by oxygen limitation. We report that an extracytoplasmic function σ factor, σC, is responsible for the regulation of this process. Chromatin immunoprecipitation with microarray analysis detected eight σC-binding regions in the genome, facilitating the identification of a consensus promoter sequence for σC recognition. The promoter sequences were found upstream of genes for cytochromebd, hemeasynthesis enzymes and uncharacterized membrane proteins, all of which were upregulated bysigCoverexpression. However, one consensus promoter sequence found on the antisense strand upstream of an operon encoding the cytochromebc1 complex conferred a σC-dependent negative effect on expression of the operon. The σC regulon was induced by cytochromeaa3 deficiency without modifyingsigCexpression, but not bybc1 complex deficiency. These findings suggest that σC is activated in response to impaired electron transfer via cytochromeaa3 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.

We defined the regulon of an extracytoplasmic function σ factor, σC, in Corynebacterium glutamicum, a bacterium in the phylum Actinobacteria. Upon activation in response to cytochrome aa3 deficiency, σC upregulates expression of cytochrome bd menaquinol oxidase, which has higher affinity for oxygen than cytochrome aa3-type cytochrome c oxidase, and heme a synthetic enzymes. Conversely, σC downregulates the cytochrome bc1 complex via a specific promoter on the antisense strand.

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