Depletion of the DarG antitoxin in <i>Mycobacterium tuberculosis</i> triggers the DNA‐damage response and leads to cell death

Abstract

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.