MazF6 toxin of Mycobacterium tuberculosis demonstrates antitoxin specificity and is coupled to regulation of cell growth by a Soj-like protein

Abstract

Background: Molecular programs employed by Mycobacterium tuberculosis (Mtb) for the establishment of non-replicating persistence (NRP) are poorly understood. In order to investigate mechanisms regulating entry into NRP, we asked how cell cycle regulation is linked to downstream adaptations that ultimately result in NRP. Based on previous reports and our recent studies, we reason that, in order to establish NRP, cells are halted in the cell cycle at the point of septum formation by coupled regulatory mechanisms. Results: Using bioinformatic consensus modeling, we identified an alternative cell cycle regulatory element, Soj Mtb encoded by rv1708. Soj Mtb coordinates a regulatory mechanism involving cell cycle control at the point of septum formation and elicits the induction of the MazF6 toxin. MazF6 functions as an mRNA interferase leading to bacteriostasis that can be prevented by interaction with its cognate antitoxin, MazE6. Further, MazEF6 acts independently of other Maz family toxin:antitoxin pairs. Notably, soj Mtb and mazEF6 transcripts where identified at 20, 40 and 100 days post-infection in increasing abundance indicating a role in adaption during chronic infection. Conclusions: Here we present the first evidence of a coupled regulatory system in which cell cycle regulation via Soj Mtb is linked to downstream adaptations that are facilitated through the activity of the MazEF6 TA pair.

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.…”

“…These differences in the transcript levels may be attributed to the differential stability of the transcripts or the expression of mazF is driven from multiple promoters. Similar post-transcriptional regulation of TA modules has also been observed in E. coli and during infection of macrophages and mice with Mtb 32, 41,42 .…”

“…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.…”

Activation of the chromosomally encoded mazEFBif locus of Bifidobacterium longum under acid stress

“…Several models supporting the different functions of the TA system in bacterial physiology have been proposed, including a programmed cell death model, growth-modulation model, persistence model, development model and stress tolerance module Gerdes and Maisonneuve, 2012;Van Melderen and Saavedra De Bast, 2009). In spite of the different functions that have been proposed, increasing evidence has demonstrated that TA systems encoded by chromosomes are stress-response loci that can impact overall cell physiology and help cells to cope with various stresses under unfavorable conditions (Buts et al, 2005;Pandey and Gerdes, 2005;Ramirez et al, 2013;Soo and Wood, 2013;Tamman et al, 2013). One group has reported that TA loci are highly abundant in free-living prokaryotes, whereas obligate intracellular organisms are devoid of these loci (Pandey and Gerdes, 2005).…”

“…Because TA systems participate in the stress responses of E. coli, Mycobacterium tuberculosis and Pseudomonas putida (Ramirez et al, 2013;Tamman et al, 2013;Van Melderen and Saavedra De Bast, 2009), it can be postulated that those in bifidobacteria might act as important stress-response elements. Whether there are functional TA systems in bifidobacterial chromosomes and what roles they play in cellular responses to environmental challenges have not yet been reported.…”