Dataset Information

Differential expression of a virulence factor in pathogenic and non-pathogenic mycobacteria.

ABSTRACT: The pathogenicity of mycobacterial infections depends on virulence factors that mediate survival inside host macrophages. These virulence factors are generally believed to be specific for pathogenic species and absent or mutated in non-pathogenic strains. The serine/threonine protein kinase G (PknG) mediates survival of mycobacteria within macrophages by blocking lysosomal delivery. Here we describe a gene of the non-pathogenic species Mycobacterium smegmatis that is 78% identical with pknG of Mycobacterium tuberculosis and M. bovis bacillus Calmette-Guérin (BCG). When cloned into expression vectors, the M. smegmatis pknG orthologue produced an active kinase and performed the same function as its M. bovis BCG counterpart in intracellular survival. In addition, similar levels of pknG transcripts were found in M. bovis BCG and M. smegmatis. However, virtually no translation product of chromosomal pknG could be detected in M. smegmatis both after in vitro growth and after macrophage infection. This lack of efficient translation was shown to be caused by regulatory elements in the upstream region of the M. smegmatis gene. The data reveal dramatically increased translational efficiency of a virulence gene in a pathogenic mycobacterium compared with a non-pathogenic mycobacterium suggesting that changes in expression levels may underlie evolution of pknG and other pathogenicity genes in mycobacterium.

SUBMITTER: Houben EN

PROVIDER: S-EPMC2784876 | biostudies-other | 2009 Apr

REPOSITORIES: biostudies-other

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Differential expression of a virulence factor in pathogenic and non-pathogenic mycobacteria.

Houben Edith N G EN Walburger Anne A Ferrari Giorgio G Nguyen Liem L Thompson Charles J CJ Miess Christian C Vogel Guido G Mueller Bernd B Pieters Jean J

Molecular microbiology 20090202 1

The pathogenicity of mycobacterial infections depends on virulence factors that mediate survival inside host macrophages. These virulence factors are generally believed to be specific for pathogenic species and absent or mutated in non-pathogenic strains. The serine/threonine protein kinase G (PknG) mediates survival of mycobacteria within macrophages by blocking lysosomal delivery. Here we describe a gene of the non-pathogenic species Mycobacterium smegmatis that is 78% identical with pknG of M ...[more]

PMID: 19210624

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Project description:During infection, Mycobacterium tuberculosis colonizes macrophages or necrotic granulomas, in which low pH is one of the major challenges. The PhoPR two-component regulatory system and the cytosolic redox sensor WhiB3 both play important roles in the response to low pH by M. tuberculosis However, whether close association exists between PhoPR and WhiB3 remains unclear. In this study, the positive regulation of whiB3 by PhoPR in mycobacteria was characterized. We observed that the expression patterns of the whiB3 gene under acidic conditions are different among mycobacterial species, suggesting that the regulation of whiB3 differs among mycobacteria. A sequence analysis of the whiB3 promoters (whiB3p) from M. tuberculosis and two closely related species, namely, M. marinum and M. smegmatis, showed that the whiB3p regions from M. tuberculosis and M. marinum contain a new type of PhoP box that is absent in the M. smegmatiswhiB3p Direct binding of PhoP to whiB3p from M. tuberculosis and M. marinum but not that from M. smegmatis was validated by in vitro protein-DNA binding assays. The direct activation of whiB3 by PhoPR under acidic conditions was further verified by reverse transcription-quantitative PCR (qRT-PCR) analysis in M. marinum Moreover, mutating the residues important for the phosphorylation pathway of PhoPR in M. marinum abolished the activation of whiB3 expression by PhoPR under acidic conditions, suggesting that low pH triggers the phosphorylation of PhoPR, which in turn activates the transcription of whiB3 Since the PhoP box was only identified in whiB3p of pathogenic mycobacteria, we suggest that the PhoPR-whiB3 regulatory pathway may have evolved to facilitate mycobacterial infection.IMPORTANCE The low pH in macrophages is an important barrier for infection by microbes. The PhoPR two-component regulatory system is required for the response to low pH and plays a role in redox homeostasis in Mycobacterium tuberculosis WhiB3, a cytosolic redox-sensing transcriptional regulator, is also involved in these processes. However, there is no direct evidence to demonstrate the regulation of WhiB3 by PhoPR. In this study, we found that PhoPR directly activates whiB3 expression in response to low pH. An atypical PhoP box in the whiB3 promoters has been identified and is only found in pathogenic mycobacteria, which suggests that the PhoPR-whiB3 regulatory pathway may facilitate mycobacterial infection. This study provides novel information for further characterization of the PhoPR regulon.

Dataset Information

Differential expression of a virulence factor in pathogenic and non-pathogenic mycobacteria.

Publications

Differential expression of a virulence factor in pathogenic and non-pathogenic mycobacteria.

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