Differential Gene Expression in Response to Exposure to Antimycobacterial Agents and Other Stress Conditions among SevenMycobacterium tuberculosis whiB-Like Genes

Abstract

The seven Mycobacterium tuberculosis whiB-like genes encode small proteins postulated to be transcriptional regulators. A systematic real-time reverse transcription-PCR analysis following exposure to antibiotics and a variety of growth and in vitro stress conditions indicates differential, and in some cases dramatic, transcription modulations for the different M. tuberculosis whiB family members. This information together with biochemical analyses of the whiB1 to whiB7 gene products will be important for understanding the biology of this novel family of proteins in mycobacteria and related actinomycetes.Upon infection, Mycobacterium tuberculosis has the ability to adapt to many different environments within the host organism. Tubercle bacilli are able to avoid immune system detection and persist inside the host for decades. Many of the conditions to which the bacteria are exposed, such as the acidic environment within the phagolysosomal compartment, are harsh (14). In the lung, there is a recruitment of activated macrophages to the infection site, and these, along with other immune cells, contain the infection by forming a tuberculous granuloma (49). M. tuberculosis is adept at surviving within the hypoxic and fatty acid-rich granulomatous environment (8), a facet critical to its ability to persist despite immune pressure (25,28). Moreover, tubercle bacilli can survive for long periods of exposure to low-nutrient conditions, such as may occur within a granuloma (4, 34), as well as temperature and oxidative stress which may act to disrupt the M. tuberculosis cell membrane. The bacterium also has a remarkable tolerance to a wide range of antibiotics (12,26). To survive, the organism must sense and respond to exogenous stress conditions. Hence, differential expression of transcriptional regulators, which control sets of genes that respond to environmental stimuli, is an important mechanism of stress survival.A family of genes which may be key transcriptional regulators in M. tuberculosis is the whiB gene family. The whiB-like genes are exclusive to the actinomycetes, such as Mycobacterium and Streptomyces spp., and are absent from all other organisms studied thus far (9, 44). whiB was identified in Streptomyces coelicolor as an essential gene for sporulation of aerial hyphae (9), and early sporulation genes were identified by morphological studies of a collection of mutants unable to form normal gray spore pigment (17). Because their aerial mycelium remained white upon prolonged incubation, these mutants were designated whi mutants. S. coelicolor whiB encodes an 87-amino-acid polypeptide with attributes suggesting that it may be a DNA binding protein (9). S. coelicolor WhiB and its related homologues, including S. coelicolor WhiD, each contain four cysteine residues, a feature common in metalcoordinating DNA binding proteins (33). Indeed, a recent study has found that Sc WhiD binds a [4Fe-4S] cluster under anaerobic conditions similar to the situation with Escherichia coli DNA binding regulators SoxR and Fnr (6,10,...

Dissecting transcription regulatory pathways through a new bacterial one-hybrid reporter system

“…Our current study found that WhiB3 could bind directly with the promoter sequences of most in vivo-induced genes (Tables 1, 2). Previous findings have shown that WhiB3 binds with the major sigma factor RpoV and can be induced by several stressful in vitro stimuli (Steyn et al 2002;Geiman et al 2006). Therefore, our findings, together with those from previous reports, support a model in which M. tuberculosis WhiB3 is a core regulator for both metabolic switching and intracellular redox sensing.…”

“…Based on the redox-sensing properties of WhiB3, together with the growth properties of its mutant on carbon-limiting media, WhiB3 has been suggested to play important roles in the regulation of both metabolic and redox switchover events (Singh et al 2007). Thus, the proteins of the WhiB family, which can be induced by several stressful in vivo stimuli (Morris et al 2005;Banaiee et al 2006;Geiman et al 2006), may facilitate an integrated transcriptional response to multiple stresses encountered within the phagosome. Indeed, the M. bovis whiB3 mutant was completely attenuated for growth in guinea pigs (Steyn et al 2002), although the H37Rv whiB3 gene was not essential for growth in mouse and guinea pig models.…”

Regulation of the expression of whiB1 in Mycobacterium tuberculosis: role of cAMP receptor protein

“…2(b), the b-galactosidase specific activity resulting from whiB1 promoter expression at different growth phases remained constant, thus indicating that whiB1 is expressed constitutively in M. tuberculosis. Recently, a similar pattern of whiB1 expression was observed in M. tuberculosis by Geiman et al (2006) by using the RT-PCR method.…”

Global transcriptional response to vancomycin in Mycobacterium tuberculosis

“…This gene has been recently shown to be induced after exposure to surface stress (SDS, ethanol), oxidative stress (diamide, cumene peroxide) and heat shock (Geiman et al, 2006). Members of this family have been shown to be involved in differentiation, spore formation and septation in Streptomyces (Soliveri et al, 2000).…”