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Mol Microbiol. 2018 Feb;107(3):312-329. doi: 10.1111/mmi.13883. Epub 2017 Dec 8.

Extracytoplasmic function sigma factor σD confers resistance to environmental stress by enhancing mycolate synthesis and modifying peptidoglycan structures in Corynebacterium glutamicum.

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Research institute of Innovative Technology for the Earth (RITE), 9-2 Kizugawa, Kyoto 619-0292, Japan.
Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5, Takayama, Ikoma, Nara 630-0101, Japan.


Mycolates are α-branched, β-hydroxylated, long-chain fatty acid specifically synthesized in bacteria in the suborder Corynebacterineae of the phylum Actinobacteria. They form an outer membrane, which functions as a permeability barrier and confers pathogenic mycobacteria to resistance to antibiotics. Although the mycolate biosynthetic pathway has been intensively studied, knowledge of transcriptional regulation of genes involved in this pathway is limited. Here, we report that the extracytoplasmic function sigma factor σD is a key regulator of the mycolate synthetic genes in Corynebacterium glutamicum in the suborder. Chromatin immunoprecipitation with microarray analysis detected σD -binding regions in the genome, establishing a consensus promoter sequence for σD recognition. The σD regulon comprised acyl-CoA carboxylase subunits, acyl-AMP ligase, polyketide synthase and mycolyltransferases; they were involved in mycolate synthesis. Indeed, deletion or overexpression of sigD encoding σD modified the extractable mycolate amount. Immediately downstream of sigD, rsdA encoded anti-σD and was under the control of a σD -dependent promoter. Another σD regulon member, l,d-transpeptidase, conferred lysozyme resistance. Thus, σD modifies peptidoglycan cross-linking and enhances mycolate synthesis to provide resistance to environmental stress.

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