Toxin–antitoxin vapBC locus participates in formation of the dormant state in M ycobacterium smegmatis

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 M ycobacterium 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 .