The Three RelE Homologs of Mycobacterium tuberculosis Have Individual, Drug-Specific Effects on Bacterial Antibiotic Tolerance

Abstract

In Escherichia coli, expression of the RelE and HipA toxins in the absence of their cognate antitoxins has been associated with generating multidrug-tolerant "persisters." Here we show that unlike persisters of E. coli, persisters of Mycobacterium tuberculosis selected with one drug do not acquire cross-resistance to other classes of drugs. M. tuberculosis has three homologs of RelE arranged in operons with their apparent antitoxins. Each toxin individually arrests growth of both M. tuberculosis and E. coli, an effect that is neutralized by coexpression of the cognate antitoxin. Overexpression or deletion of each of the RelE toxins had a toxin-and drug-specific effect on the proportion of bacilli surviving antibiotic killing. All three toxins were upregulated in vivo, but none of the deletions affected survival during murine infection. RelE2 overexpression increased bacterial survival rates in the presence of rifampin in vitro, while deletion significantly decreased survival rates. Strikingly, deletion of this toxin had no discernible effect on the level of persisters seen in rifampin-treated mice. Our results suggest that, in vivo, RelE-generated persisters are unlikely to play a significant role in the generation of bacilli that survive in the face of multidrug therapy or in the generation of multidrug-resistant M. tuberculosis.

MazF ribonucleases promote Mycobacterium tuberculosis drug tolerance and virulence in guinea pigs

“…Consistent with observations of other TA systems, we also observed relative abundance of mazF transcripts in comparison with mazE transcripts (Fig. 1c-e) 32,41,42 . Compared with early log phase bacteria, no differences were observed in the transcript levels of mazE3, mazF3, mazE6, mazF6, mazE9 and mazF9 in mid-log and late-log growth stages (Fig.…”

“…4d, paired (two-tailed) t-test Po0.05). This reduction in bacterial counts was higher than those observed for Mtb strains lacking either mazF3, mazF9, Rv1246c (relE1), relE2 or Rv3358 (relE3), which maintained bacterial loads at levels comparable with those of the parental strain in murine infections 32 .…”

“…TA systems are differentially induced under adverse environmental conditions such as amino acid starvation, oxidative stress and hypoxia, and in macrophages and host tissues 24,32,[40][41][42] . The present study was conducted to investigate the role of MazEF TA systems in the physiology, drug-tolerance and virulence of Mtb.…”

“…The construction of an Rv1102c (DmazF3) knockout strain and its characterization in a murine model of tuberculosis has been reported 32 . In the present study, various single-, For qRT-PCR analysis, mRNA was isolated from early-log, mid-log, late-log and NRP cultures of Mtb.…”

“…Besides ribonuclease activity, MazF4 also affects bacterial survival by modulating DNA topoisomerase activity 30 . The overexpression of Rv2866 (RelE2) results in cell elongation in Msm and RelE toxins also contribute to drug tolerance in vitro 31,32 . The HigB toxin targets tmRNA, IdeR and Zur-regulated transcripts, and its activity is regulated by a SecB-like chaperone, Rv1957 (refs 33,34).…”