Deletion of the Mycobacterium tuberculosis α-Crystallin-Like hspX Gene Causes Increased Bacterial Growth In Vivo

Abstract

Hypervirulent mutants of Mycobacterium tuberculosis, whose growth rates are higher in vivo, have now been reported to have mutations in both regulatory and structural genes, but the basis for this unusual phenotype is not understood. One hypervirulence gene, dosR (devR, Rv2031c), activates transcription of approximately 50 genes in this pathogen in response to hypoxia and nitric oxide stress. The most dramatic activation (ϳ80-fold) is activation of the hspX (acr, Rv2031c) gene, which encodes a 16-kDa ␣-crystallin-like protein that is a major antigen. In this study we found that a ⌬acr mutant exhibited increased growth following infection of BALB/c mice in vivo and in both resting and activated macrophages in vitro (as measured by the number of CFU). The increased growth in macrophages was equal to that of a ⌬dosR mutant, while introduction of a constitutively expressed hspX gene reduced the ⌬dosR virulence to wild-type levels. These results suggest that the increased number of CFU of the ⌬dosR mutant was largely due to loss of hspX expression. We also confirmed that constitutive expression of hspX slows growth in vitro, and we propose that hspX plays an active role in slowing the growth of M. tuberculosis in vivo immediately following infection.

Profiling the Proteome of Mycobacterium tuberculosis during Dormancy and Reactivation

“…35 S]methionine labeling studies Hu et al, (2006) showed that in dormant MTB culture maintained in unstirred screw-cap tubes for 50 days, protein synthesis decreased by 98% (42). Eighty-six proteins involved in protein synthesis were detected in our study.…”

“…This protein is implicated in the survival of MTB inside macrophages (15). The biology of alpha-crystallin 1 is complex as evidenced by the adverse effect of the gene knockout on growth (69). Overexpression of acr slows down the growth rate of MTB and the autolysis of post-stationary phase cultures (15).…”

Transcriptomic Analysis Identifies Growth Rate Modulation as a Component of the Adaptation of Mycobacteria to Survival inside the Macrophage

“…The hspX gene has been found to be upregulated during the stationary phase (37), in several models of dormancy (23,37), and during the growth of M. tuberculosis in macrophages (30), mice (31), and lung specimens from patients with TB (34). Recent work has demonstrated that HspX has a role in slowing the growth of M. tuberculosis both in vitro and in vivo (14). An hspX gene replacement mutant of M. tuberculosis exhibited increased growth in macrophages and also in a mouse model, whereas overexpression of the hspX gene resulted in a reduction in the growth rate of M. tuberculosis in vitro (14,39).…”

“…Recent work has demonstrated that HspX has a role in slowing the growth of M. tuberculosis both in vitro and in vivo (14). An hspX gene replacement mutant of M. tuberculosis exhibited increased growth in macrophages and also in a mouse model, whereas overexpression of the hspX gene resulted in a reduction in the growth rate of M. tuberculosis in vitro (14,39). The demonstration that expression of hspX was induced during slow growth in a carbon-limited chemostat provides further evidence that this chaperone plays a role in reducing the growth rate of M. tuberculosis.…”

Expression of the Mycobacterium tuberculosis acr -Coregulated Genes from the DevR (DosR) Regulon Is Controlled by Multiple Levels of Regulation

“…Previous studies have shown that expression of the 16-kDa M. tuberculosis ␣-crystallin protein, Acr, encoded by acr (also called hspX, Rv2031c) occurs in vivo (13,18,43,53) and is rapidly induced during stationary-phase growth, in unagitated submerged cultures, and in oxygen-limiting or nitric oxide (NO)-enriched microenvironments (9,10,17,22,34,42,48,52,53). acr is a member of the DevR (also called DosR) "dormancy" regulon that includes genes that are positively regulated in response to hypoxia and/or low levels of NO (28,31,41,42,47).…”