Chip-chip analysis of C. glutamicum SigD

(Coryno)mycolate is a α-branched, β-hydroxylated long-chain fatty acid specifically synthesized in bacteria in the suborder Corynebacterineae of the phylum Actinobacteria. It forms an outer membrane and functions as a permeability barrier conferring pathogenic mycobacteria to resistance to antibiotics. Whereas mycolate biosynthetic pathway has been intensively studied, the studies on the transcriptional regulation of genes involved in the pathway are limited. Here, we report that the previously uncharacterized extracytoplasmic function σ 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 comprises acyl-CoA carboxylase subunits, acyl-AMP ligase, polyketide synthase, and mycolyltransferases, all of which are involved in mycolate synthesis. Actually, deletion or overexpression of sigD encoding σD modified the amount of extractable mycolate. 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 cell wall composition and enhances mycolate synthesis to provide resistance to environmental stress. ChIP-chip analyses using a strain expressing the FLAG-tagged SigD in the background of the wild type at the exporenatial phases. Two independent experiments were performed.