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

Abstract

Bacteria modify their expression of different terminal oxidases in response to oxygen availability. Corynebacterium glutamicum, a facultative anaerobic bacterium of the phylum Actinobacteria, possesses aa3 -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 σ factor, σ(C) , is responsible for the regulation of this process. Chromatin immunoprecipitation with microarray analysis detected eight σ(C) -binding regions in the genome, facilitating the identification of a consensus promoter sequence for σ(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 bc1 complex conferred a σ(C) -dependent negative effect on expression of the operon. The σ(C) regulon was induced by cytochrome aa3 deficiency without modifying sigC expression, but not by bc1 complex deficiency. These findings suggest that σ(C) is activated in response to impaired electron transfer via cytochrome aa3 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.

Assignment of sigma factors of RNA polymerase to promoters in Corynebacterium glutamicum

“…Expression of the genes regulated by σ C has recently been described (Toyoda and Inui 2016a). We selected the promoter of the C. glutamicum ATCC 13032 cg2556 gene encoding an uncharacterized iron-regulated membrane protein (corresponding to the cgR_2208 gene in the sequence of C. glutamicum R; Toyoda and Inui 2016a) to test sigma dependency of its promoter.…”

“…We selected the promoter of the C. glutamicum ATCC 13032 cg2556 gene encoding an uncharacterized iron-regulated membrane protein (corresponding to the cgR_2208 gene in the sequence of C. glutamicum R; Toyoda and Inui 2016a) to test sigma dependency of its promoter. In vitro transcription assays confirmed that cg2556 transcription is σ C -specific (Fig.…”

“…4Assignment of a sigma factor to the P cg2556 promoter. a Sequence of the cg2556 ( cgR_2208 ) promoter (Toyoda and Inui 2016a). The −35 and −10 sequence elements are in bold , the transcriptional start site is underlined .…”

“…The σ C regulon that is induced in response to defects in aerobic respiration has been recently described (Toyoda and Inui 2016a). Eight σ C -specific promoters were found, and their consensus sequence was defined as −35 GGAAAC and −10 CGACT.…”

Use of In Vitro Transcription System for Analysis of Corynebacterium glutamicum Promoters Recognized by Two Sigma Factors

“…However, some C. glutamicum promoters were defined as r M -dependent by some authors [12] whereas as r H -dependent by others [5]. Very recently, a consensus sequence of several promoters of r C -controlled genes was deduced [24]. We report here the evidence of overlap of C. glutamicum sigma factors r A and r B , or r H and r E in recognizing specific promoters, obtained by use of C. glutamicum in vitro transcription system.…”