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

Abstract

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.