The ECF-type sigma factor SigM of Corynebacterium glutamicum ATCC 13032 is involved in transcription of disulfide stress-related genes

Institut für Genomforschung und Systembiologie, Centrum für Biotechnologie, Universität Bielefeld, Postfach 100131, 33501 Bielefeld, Germany and Lehrstuhl für Genetik, Fakultät für Biologie, Universität Bielefeld, Postfach 100131, 33501 Bielefeld, Germany

^* To whom correspondence should be addressed. Email: Joern.Kalinowski{at}Genetik.Uni-Bielefeld.DE.

	Abstract

The gene of the extra-cytoplasmic function (ECF) sigma factor SigM was deleted in the chromosome of the gram-positive soil bacterium Corynebacterium glutamicum to elucidate the role of the SigM protein in regulation of gene expression. Comparative DNA microarray hybridizations of the C. glutamicum wild-type and the sigM-deficient mutant C. glutamicum DN1 revealed 23 genes with enhanced expression in the sigM-proficient strain, encoding functions in the assembly of iron-sulfur clusters (suf operon), thioredoxin reductase (trxB), thioredoxins (trxC, trxB1), chaperones (groES, groEL, clpB) and proteins involved in the heat-shock response (hspR, dnaJ, grpE). Deletion of the sigM gene rendered the C. glutamicum cells more sensitive to heat, cold and the presence of the thiol-oxidant diamide. Transcription of the sigM gene increased under different stress conditions, including heat-shock, cold-shock and disulfide stress caused by diamide treatment, suggested a regulatory role of SigM under thiol-oxidative stress conditions. Stress-responsive promoters were determined upstream of the suf operon and of the trxB, trxC and trxB1 genes. The deduced SigM consensus promoter is characterized by the -35 hexamer gGGAAT and the -10 hexamer YGTTGR. Transcription of the sigM gene is apparently controlled by the ECF sigma factor SigH, since a sigH mutant was unable to enhance expression of sigM and the SigM regulon under thiol-oxidative stress conditions. A typical SigH-responsive promoter was mapped upstream of the sigM gene. The ECF sigma factor SigM is apparently part of a regulatory cascade and its transcription is controlled by SigH under conditions of thiol-oxidative stress.