A mycobacterial extracytoplasmic function sigma factor involved in survival following stress

Abstract

The extracytoplasmic function (ECF) sigma factors constitute a diverse group of alternative sigma factors that have been demonstrated to regulate gene expression in response to environmental conditions in several bacterial species. Genes encoding an ECF sigma factor of Mycobacterium tuberculosis, Mycobacterium avium, and Mycobacterium smegmatis, designated sigE, were cloned and analyzed. Southern blot analysis demonstrated the presence of a single copy of this gene in these species and in Mycobacterium bovis BCG, Mycobacterium leprae, and Mycobacterium fortuitum. Sequence analysis showed the sigE gene to be highly conserved among M. tuberculosis, M. avium, M. smegmatis, and M. leprae. Recombinant M. tuberculosis SigE, when combined with core RNA polymerase from M. smegmatis, reconstituted specific RNA polymerase activity on sigE in vitro, demonstrating that this gene encodes a functional sigma factor. Two in vivo transcription start sites for sigE were also identified in M. smegmatis and M. bovis BCG. Comparison of wild-type M. smegmatis with a sigE mutant strain demonstrated decreased survival of the mutant under conditions of high-temperature heat shock, acidic pH, exposure to detergent, and oxidative stress. An inducible protective response to oxidative stress present in the wild type was absent in the mutant. The mycobacterial SigE protein, although nonessential for viability in vitro, appears to play a role in the ability of these organisms to withstand a variety of stresses.Regulation of gene expression in response to the extracellular environment is an adaptive response that is required for bacterial replication and survival. Alternative sigma factors have been demonstrated to play an important role in the coordinate regulation of gene expression in bacteria undergoing major adaptive changes in physiology, well-studied examples of which include sporulation in Bacillus subtilis and the stationary-phase response in Escherichia coli (11,14,36).Sigma factors of the sigma-70 class have been grouped into families based on conservation of sequence and function across bacterial species (24,25). An extended family of alternative sigma factors, the SigE family, has been found to regulate gene expression required for diverse functions in several bacterial species, including survival following high-temperature heat shock in E. coli and alginate production in Pseudomonas aeruginosa (8,19,30,31). In many cases, these SigE sigma factors regulate bacterial gene expression in response to the extracellular environment and have been referred to as extracytoplasmic function (ECF) sigma factors (24).In pathogenic bacteria, regulation of gene expression during the course of infection is necessary to survive in the environment of the host organism. Examples of alternative sigma factor-regulated gene expression that play a role bacterial pathogenesis include regulation of alginate production by AlgU resulting in mucoid P. aeruginosa in patients with cystic fibrosis and regulation of the plasmid-encoded spv virulence genes of Sal...

Evidence for complex interactions of stress-associated regulons in an mprAB deletion mutant of Mycobacterium tuberculosis

“…We identified an additional start site, TSP4, which is coincident with the putative start codon of sigE, and upstream of TSP3 (Fig. 3a, b, g), supporting reports that sigE is smaller than predicted (Raman et al, 2001;Wu et al, 1997). TSP4 is activated by SDS stress in H37Rv, in an MprA-dependent manner, as indicated by the reduced intensity of bands for Rv-D981 (Fig.…”

“…3a): TSP1 and TSP2 in M. bovis BCG (Wu et al, 1997), and a SigH-dependent TSP (TSP3) (Raman et al, 2001) located within the predicted coding region of M. tuberculosis sigE (Cole et al, 1998). We identified an additional start site, TSP4, which is coincident with the putative start codon of sigE, and upstream of TSP3 (Fig.…”

“…Similar to rpoE of Escherichia coli (Mecsas et al, 1993;Tam & Missiakas, 2005), M. tuberculosis sigE may, therefore, be induced by envelope stress, but the mechanisms involved have not been determined. Deletion of sigE in mycobacteria is associated with reduced resistance to SDS and oxidative stress, decreased growth in macrophages (Manganelli et al, 2001;Wu et al, 1997), and reduced growth in mice (Ando et al, 2003;Manganelli et al, 2004).…”

Surviving the Acid Test: Responses of Gram-Positive Bacteria to Low pH

“…One of these, SigE, influences survival following stress in a number of mycobacteria, as demonstrated by the enhanced rate of killing of an M. smegmatis sigE mutant at pH 4 (252).…”

NUCLEOSIDE DIPHOSPHATE KINASE GENE IS EXPRESSED THROUGH MULTIPLE TRANSCRIPTS IN Mycobacterium smegmatis

“…However, SigC is absent in M. smegmatis [41] and therefore regulation of P2 might be by some unknown factor. The M. smegmatis sigE promoter P2 [42], M. tuberculosis sigH promoter P1 [43], Mycobacterium bovis BCG sigE promoters, P1 and P2 [42], tsB promoter of hsp60 [44] and of groEL1 [45], and the H2O2-inducible P1 promoter of ahpC of Mycobacterium leprae [46] are some of the examples of C group mycobacterial promoters. Many identified mycobacterial promoters often show no match with the consensus of any identified sigma factors of M. tuberculosis [29].…”