The Extra Cytoplasmic Function Sigma Factor σ ^E Is Essential for Mycobacterium tuberculosis Virulence in Mice

Abstract

The virulence of a Mycobacterium tuberculosis H37Rv sigE mutant was studied in immunodeficient and immunocompetent mice. The mutant was strongly attenuated in both animal models and induced formation of granulomas with different characteristics than those induced by the wild-type strain.During infection, bacteria often face different environments which result from the site in which the pathogen resides as well as activation of the host's immune response. To be successful, a pathogen must be able to adapt quickly to these differing milieus. Most bacterial adaptive mechanisms are based on the regulation of gene expression, which consequently plays a very important role in bacterial pathogenesis (13).Sigma factors play a major role in the regulation of bacterial gene expression. These proteins are interchangeable RNA polymerase subunits that are responsible for promoter recognition. Bacteria usually have a principal sigma factor, usually constitutively expressed, which is responsible for the transcription of essential housekeeping genes, and a number of alternative sigma factors that are transcriptionally and/or posttranslationally activated in response to specific environmental signals (14). The Mycobacterium tuberculosis genome encodes 13 putative sigma factors, 10 of which belong to the extra cytoplasmic function (ECF) family (4, 6). In previous work, our investigators studied the variation of factor gene expression in response to different environmental stresses and found that sigB and sigE were strongly induced after exposure to detergent-induced surface stress. The same two genes, together with sigH, were also induced after heat shock and after exposure to the thiol-specific oxidizing agent diamide (8, 9). Our investigators recently characterized two M. tuberculosis mutants lacking the ECF factors E and H . These mutants were sensitive to various environmental stresses; moreover, the sigE mutant showed a decreased ability to grow inside macrophages. Using DNA microarray technology, we have studied the E and H regulons and have identified several genes that are under direct or indirect control of these factors (9, 10). Interestingly, it has been recently reported that the M. tuberculosis sigE regulon is activated after phagocytosis (12). A , F , and the ECF factor H have a role in M. tuberculosis virulence, as shown in animal models of infection. A Mycobacterium bovis mutant with a mutated sigA was attenuated for virulence in guinea pigs (5), while an M. tuberculosis sigF strain was shown to be attenuated in immunocompetent mice (3). M. tuberculosis mutants lacking sigH produced a reduced immunopathology in infected animals (7), despite the observation that the growth kinetics in their organs were similar to that of the wild-type (wt) strain (7, 9).In the experiments described in this communication, we have studied the M. tuberculosis sigE mutant ST28 (10) in two different mouse models of infection: immunocompetent BALB/c mice and severe combined immunodeficient (SCID) mice, which lack functional B and T cells...

Examination of Mycobacterium tuberculosis sigma factor mutants using low-dose aerosol infection of guinea pigs suggests a role for SigC in pathogenesis

“…SigE, however, was reported to be required for survival of H37Rv in macrophages (Manganelli et al, 2001). In addition, a sigE mutant persisted less effectively than the H37Rv parent strain in the lungs, spleen and liver of BALB/c mice, and mice infected with the mutant survived longer than those infected with the parent strain (Manganelli et al, 2004). Interestingly, while C3H/HeJ mice infected with a sigE mutant of the CDC1551 strain also survived longer than those infected with the parent strain, the mutant was not impaired for lung persistence (Ando et al, 2003).…”

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

“…The expression of SigE-regulated genes (Manganelli et al, 2004) was evaluated in SDS-treated and control cultures of H37Rv and Rv-D981, using array analyses or real-time PCR (qPCR). For each gene, results show fold induction under SDS compared to the control sample for the same strain.…”

“…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).…”

Evolution of the Mycobacterial SigK Regulon

“…This capacity to persist in the host, despite the dynamic alterations effected by the host immune response, testifies to an evolved capacity of the organism to regulate its genetic expression to the conditions encountered during infection. Indeed, a number of studies have demonstrated that disruption of M. tuberculosis regulatory elements, such as sigma factors, results in reduced virulence in experimental models (21,28,30).The determination of genomic sequences for a number of nonpathogenic mycobacteria has revealed that homologues of many genes, including regulatory elements, are often present in organisms that are not virulent to humans. For instance, comparative analysis has demonstrated conservation of biochemical pathways and a secretory system important for full virulence of M. tuberculosis (7,10).…”

“…This capacity to persist in the host, despite the dynamic alterations effected by the host immune response, testifies to an evolved capacity of the organism to regulate its genetic expression to the conditions encountered during infection. Indeed, a number of studies have demonstrated that disruption of M. tuberculosis regulatory elements, such as sigma factors, results in reduced virulence in experimental models (21,28,30).…”