The sigma factors of Mycobacterium tuberculosis: regulation of the regulators

Abstract

One of the important determinants of virulence of Mycobacterium tuberculosis is adaptation to adverse conditions encountered in the host cells. The ability of Mycobacterium to successfully adapt to stress conditions is brought about by the expression of specific regulons effected by a repertoire of σ factors. The induction and availability of σ factors in response to specific stimuli is governed by a complex regulatory network comprising a number of proteins, including σ factors themselves. A serine–threonine protein kinase‐mediated signaling pathway adds another dimension to the mycobacterial σ factor regulatory network. This review highlights the recent advances in understanding mycobacterial σ factors, their regulation and contribution to bacterial pathogenesis.

Latent Tuberculosis Infection: Myths, Models, and Molecular Mechanisms

“…The temporal expression of specific regulons controlled by one or more alternate sigma factors likely allows M. tuberculosis to survive during multiple phases of TB infection. Expression of the M. tuberculosis factors H , E , and B can be triggered by either H or E (268,269). A growing body of literature indicates that these sigma factors are induced in response to several different in vitro conditions mimicking in vivo stresses faced by the pathogen during the various stages of infection and disease (263)(264)(265)(266)(267)270).…”

Identification of small RNAs in Mycobacterium smegmatis using heterologous Hfq

“…An extra band of 70 nt was only detected at the stationary phase, suggesting further processing of the sRNAs into a shorter sRNAs in response to the nutrient-depleted environment. Based on the presence of putative binding sites, expression of the sRNAs is likely to be regulated by different sigma factors under a variety of stress conditions including nutrient deprivation at stationary phase (Sachdeva et al 2010).…”

“…The transcription start sites of the sRNAs were predicted by searching for consensus binding sites for sigma factor A, B, or F using information provided by Sachdeva et al (2010). The sequences of detected sRNAs were proposed according to the predicted transcription start sites and the size detected on Northern blots.…”

Avaliação da virulência micobacteriana e modulação da resposta imune durante a infecção por isolados clínicos de Mycobacterium bovis e Mycobacterium tuberculosis.

“…A patogenicidade é entendida como a capacidade de um agente invasor em causar doença, com suas formas clínicas no hospedeiro, e a virulência é a capacidade patogênica de um microrganismo, medida pela mortalidade que ele induz e/ou por sua habilidade em invadir tecidos do hospedeiro. Diversos fatores gênicos, protéicos e lipídicos podem induzir virulência a um patógeno (Fratti et al, 2003;Ganguly et al, 2008;Sachdeva et al, 2010).…”

“…Tais fatores envolvidos em mecanismos de reprogramação transcricional, baixo metabolismo catalítico e capacidade imunomodulatora são responsáveis pelo sucesso do M. tuberculosis em adaptar-se ao hospedeiro (Sachdeva et al, 2010). O sequenciamento completo do cromossomo circular da cepa H37Rv de M. tuberculosis em 1998 por foi de suma importância para auxiliar a compreensão acerca da patogenia induzida pelo complexo M. tuberculosis (Cole e Barrell, 1998; (Steyn et al, 2002;Wu et al, 2004).…”