Toxin-antitoxinvapBClocus participates in formation of the dormant state inMycobacterium smegmatis

Abstract

Toxin-antitoxin (TA) loci are widely spread in bacterial plasmids and chromosomes. Toxins affect important functions of bacterial cells such as translation, replication and cell-wall synthesis, whereas antitoxins are toxin inhibitors. Participation in formation of the dormant state in bacteria is suggested to be a possible function of toxins. Here we show that overexpression of VapC toxin in Mycobacterium smegmatis results in development of morphologically distinct ovoid cells. The ovoid cells were nonreplicating and revealed a low level of uracil incorporation and respiration that indicated their dormant status. To validate the role of VapBC in dormancy formation, we used a model of dormant, 'nonculturable' (NC) M. smegmatis cells obtained in potassium-limited conditions. Overexpression of VapB antitoxin prevented transition to dormancy, presumably due to a decreased level of the free VapC protein. Indeed, this effect of the VapB was neutralized by coexpression of the cognate VapC as a part of the vapBC operon. In summary, these findings reveal participation of vapBC products in formation of the dormant state in M. smegmatis.

The Mycobacterium tuberculosis relBE toxin:antitoxin genes are stress-responsive modules that regulate growth through translation inhibition

“…1A). It has recently been demonstrated that Rv2866 (relG) causes mycobacterial cells to become filamentous (Miallau et al, 2013), while the V apC M.smegmatis toxin potentiates the development of ovoid cells (Demidenok et al, 2014). The polar expansion of mycobacterial cells following relE Mtb expression, and the elongation following relG expression, suggest that Rel Mtb toxins impact lipid biosynthesis, cell envelope assembly, and/or cell division.…”

Structural and functional studies of theMycobacterium tuberculosisVapBC30 toxin-antitoxin system: implications for the design of novel antimicrobial peptides

“…M. tuberculosis is the causative agent of tuberculosis and contains an unusually high number of VapBC systems ( 30 ). The VapBC system, which is implicated in dormant state formation ( 31 ), virulence ( 58 ), and stress response ( 59 ), is an interesting target for the rational design of an antimicrobial peptide against tuberculosis ( 26 ). Via biochemical analysis, we confirmed that M. tuberculosis VapC30 is an Mg 2+ and Mn 2+ dependent ribonuclease that inhibits cellular growth.…”

“…In M. tuberculosis , more than half of the TA systems belong to the VapBC family (47 of 88 putative TA systems) ( 30 ), and vapBC loci are tightly associated with virulence factors and pathogenicity factors ( 18 ). The VapBC family may therefore contribute to the extreme persistence and pathogenic success of M. tuberculosis ( 31 ). Although efforts to develop antimicrobial drugs based on TA systems are emerging, antimicrobial peptides based on a structural rationale remain limited to the toxin structure of Bacillus anthracis MoxT ( 32 ).…”

Relationship between the Viable but Nonculturable State and Antibiotic Persister Cells

“…In a more concrete example, E. coli mutants of the HipB antitoxin but with functional HipA toxin were nonculturable altogether (100). Demidenok and colleagues showed that overexpression of the VapB antitoxin prevented cells from entering the VBNC state, while overexpression of the VapC toxin induced the VBNC state (108). Similarly, overexpression of the MParE2 toxin led to a decline in culturability due to entry into the VBNC state (109).…”