The alternative sigma factor SigF of Mycobacterium smegmatis is required for survival of heat shock, acidic pH and oxidative stress

Abstract

The alternative sigma factor SigF of Mycobacterium tuberculosis has been characterized in detail as a general-stress, stationary-phase sigma factor involved in the virulence of the bacterium. While a homologous gene has been annotated in the genome of the fast-growing Mycobacterium smegmatis, little experimental evidence is available on the function of this gene. Here, we demonstrate that SigF of M. smegmatis is required for resistance to hydrogen peroxide, heat shock and acidic pH, but not for survival in human neutrophils. No difference in sensitivity to isoniazid was observed between the wild-type strain and the DsigF mutant, suggesting that SigFmediated resistance to hydrogen peroxide was via a pathway independent of KatG or AhpC. RT-PCR and 59-RACE (rapid amplification of cDNA ends) analyses showed that sigF of M. smegmatis was co-transcribed with rsbW (thought to encode an anti-sigma factor for SigF) and MSMEG_1802 (unknown function) and was expressed from two promoters, one upstream of MSMEG_1802 and the second upstream of rsbW. Analysis of transcriptional lacZ fusion constructs in the sigF-deletion background revealed that the MSMEG_1802 promoter was dependent on SigF for expression. Moreover, MSMEG_1802-lacZ was induced twofold upon entry into stationary phase, while exposure of exponentially growing cultures to various stress conditions (e.g. heat, cold, ethanol, hydrogen peroxide or different pH values) did not lead to induction of MSMEG_1802-lacZ. Expression of rsbW-lacZ was independent of SigF and remained constant throughout the growth cycle and under various stress conditions unless the bacteria were challenged with D-cycloserine.

Pigments and Pathogenesis

“…In M. smegmatis, exposure to acidity transcriptionally upregulates the homologue of this promoter region [17]. In addition, at least for M. smegmatis, pigment production is thought to be controlled by the sigma factor SigF [24,25]. In M. smegmatis a deletion in the sigF gene resulted in a bacterium which not only cannot produce pigments, but a mutant mycobacterium sensitive to oxidative stress as well [24,26].…”

Adaptation of Mycobacterium smegmatis to nutrient depletion and its effect on esat-6 expression

“…Este es un mecanismo de transducción, en el que los factores estresantes desencadenan una respuesta a través de la expresión de los genes, que preparan a las bacterias durante el agotamiento de los recursos (6,7) . Hecho que se puede observar in vitro en la fase exponencial y son decisivos para la adaptación a las condiciones que se presenten en la fase estacionaria y sobrevivir (8) .…”

“…Los bacilos tuberculosos responden a situaciones de estrés por agotamiento de nutrientes, pH ácido, especies reactivas de oxígeno y nitrógeno causado por su crecimiento en los macrófagos (7,8,14) . Para responder a estos estímulos, las micobacterias secretan enzimas como ESAT-6 y CFP-10 (2,15) , que en las células del hospedero, actúan en los procesos de necrosis, tales como la lisis del epitelio alveolar y membranas de los macrófagos, induce la fragmentación del ADN y la permeabilidad de la membrana de las mitocondrias (15) .…”

“…This is a transduction mechanism in which stress factors can trigger a response through gene expression, preparing the bacteria during nutrient depletion (6,7) . A fact that can be observed in vitro during the exponential phase and is decisive for adaptation to conditions present in the stationary phase and survival (8) .…”

Análise computacional da variação do potencial metabólico microbiano em metagenomas

“…As espécies mais estudadas, entre elas Mycobacterium tuberculosis, são descrita na literatura em relação a sua capacidade de responder ao estresse causado por hipóxia (RAO et al, 2008;GUMBER et al, 2009), pH altamente ácidos (GEBHARD et al, 2008;VANDAL et al, 2009;LEEAH et al, 2010;ABRAMOVITCH et al, 2011), temperatura (ANUCHIN et al, 2009) e resistência à predação (RØNN et al, 2001;BLAND et al, 2005). A baixa abundância das espécies do gênero pode ser atribuída a um aumento da temperatura da água do lago e do ar diminuindo a concentração de oxigênio dissolvido (BLAND et al, 2005;NEWTON et al, 2011).…”