NHEJ protects mycobacteria in stationary phase against the harmful effects of desiccation

The physiological role of the non-homologous end-joining (NHEJ) pathway in the repair of DNA double-strand breaks (DSBs) was examined in Mycobacterium smegmatis using DNA repair mutants (Delta recA, Delta ku, Delta ligD, Delta ku/ligD, Delta recA/ku/ligD). Wild-type and mutant strains were exposed to a range of doses of ionizing radiation at specific points in their life-cycle. NHEJ-mutant strains (Delta kU, Delta ligD, Delta ku/ligD) were significantly more sensitive to ionizing radiation (IR) during stationary phase than wild-type M. smegmatis. However, there was little difference in IR sensitivity between NHEJ-mutant and wild-type strains in logarithmic phase. Similarly, NHEJ-mutant strains were more sensitive to prolonged desiccation than wild-type M. smegmatis. A Delta recA mutant strain was more sensitive to desiccation and IR during both stationary and especially in logarithmic phase, compared to wild-type strain, but it was significantly less sensitive to IR than the Delta recA/ku/ligD triple mutant during stationary phase. These data suggest that NHEJ and homologous recombination are the preferred DSB repair pathways employed by M. smegmatis during stationary and logarithmic phases, respectively (C) 2007 Elsevier B.V. All rights reserved.