Abstract
Of the ~80 putative toxin-antitoxin (TA) modules encoded by the bacterial pathogen Mycobacterium tuberculosis (Mtb), three contain antitoxins essential for bacterial viability. One of these, Rv0060 (DNA ADP-ribosyl glycohydrolase, DarG(Mtb) ), functions along with its cognate toxin Rv0059 (DNA ADP-ribosyl transferase, DarT(Mtb) ), to mediate reversible DNA ADP-ribosylation (Jankevicius et al., 2016). We demonstrate that DarT(Mtb) -DarG(Mtb) form a functional TA pair and essentiality of darG(Mtb) is dependent on the presence of darT(Mtb) , but simultaneous deletion of both darT(Mtb) -darG(Mtb) does not alter viability of Mtb in vitro or in mice. The antitoxin, DarG(Mtb) , forms a cytosolic complex with DNA-repair proteins that assembles independently of either DarT(Mtb) or interaction with DNA. Depletion of DarG(Mtb) alone is bactericidal, a phenotype that is rescued by expression of an orthologous antitoxin, DarG(Taq) , from Thermus aquaticus. Partial depletion of DarG(Mtb) triggers a DNA-damage response and sensitizes Mtb to drugs targeting DNA metabolism and respiration. Induction of the DNA-damage response is essential for Mtb to survive partial DarG(Mtb) -depletion and leads to a hypermutable phenotype.