Characterization of homologous recombination and non-homologous end-joining in DNA double-strand break repair of Bacillus subtilis spores after exposure to ionizing radiation

The role of the two major DNA double strand break (DSB) repair mechanisms, homologous recombination (HR) and non-homologous end-joining (NHEJ), in Bacillus subtilis spore resistance to ionizing radiation had been investigated. Spores deficient in PNPase, HR- and NHEJ- mediated DNA repair were analyzed with regard to their survivability upon the exposure to X-rays and compared to the responses of B. subtilis BG214 wild-type spores. Spore resistance was observed to decrease in the following order (from the most resistant to the most sensitive ones): ΔrecQ ≥ wild-type > ΔrecN > ΔrecS > ΔrecJ > ΔpnpA > ΔrecU > ΔrecG > ΔrecO > ΔKu > ΔrecA > ΔrecF > ΔpnpA Ku > ΔrecR > ΔpnpA recA > ΔKu recA, indicating that HR and NHEJ both play a central role in protecting B. subtilis spores against potentially lethal environmental conditions. Further, it could be shown that ionizing radiation induces a significant time-delay in spore germination and subsequent outgrowth events, as demonstrated by germination profiling via well-plate-based germination assays as well as transcriptional profiling via cDNA microarray technology, suggesting the extensive expiration of repair of ionizing radiation-induced DNA damages during spore germination