Deficiency of Double-Strand DNA Break Repair Does Not Impair Mycobacterium tuberculosis Virulence in Multiple Animal Models of Infection

Mycobacterium tuberculosis persistence within its human host requires mechanisms to resist the effector molecules of host im-munity, which exert their bactericidal effects through damaging pathogen proteins, membranes, and DNA. Substantial evidence indicates that bacterial pathogens, includingM. tuberculosis, require DNA repair systems to repair the DNA damage inflicted by the host during infection, but the role of double-strand DNA break (DSB) repair systems is unclear. Double-strand DNA breaks are the most cytotoxic form of DNA damage and must be repaired for chromosome replication to proceed.M. tuberculosis elab-orates three genetically distinct DSB repair systems: homologous recombination (HR), nonhomologous end joining (NHEJ), and single-strand annealing (SSA). NHEJ, which repairs DSBs in quiescent cells, may be particularly relevant toM. tuberculosis la-tency. However, very little information is available about the phenotype of DSB repair-deficientM. tuberculosis in animal mod-els of infection. Here we testedM. tuberculosis strains lacking NHEJ (akuligD strain), HR (arecA strain), or both (arecA ku strain) in C57BL/6J mice, C3HeB/FeJ mice, guinea pigs, and a mouse hollow-fiber model of infection. We found no differ-ence in bacterial load, histopathology, or host mortality between wild-type and DSB repair mutant strains in any model of infec-tion. These results suggest that the animal models tested do not inflict DSBs on the mycobacterial chromosome, that other repair pathways can compensate for the loss of NHEJ and HR, or that DSB repair is not required forM. tuberculosis pathogenesis. Mycobacterium tuberculosis is one of the world’s most success-ful pathogens, which reflects the ability of this pathogen to adapt to the human host. M. tuberculosis is capable of persistin