Depletion Of The Darg Antitoxin In Mycobacterium Tuberculosis Triggers The Dna-Damage Response And Leads To Cell Death

Of the similar to 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.