Effects of DNA Repair and Protective Components in Bacillus subtilis Spore Resistance to Blue-Light Radiation

Abstract

Due to the high resistance and potential roles in human disease and food spoilage of spores of Firmicutes, methods for spore eradication are of significant interest for medical products, food- and health care industries and in particular methods that effectively kill spores while remaining relatively benign to humans and sensitive equipment. Intense blue-light at ~ 380 - 450 nm is one such treatment that has drawn significant interest. This work has determined the resistance of spores to blue-light under oxic and anoxic conditions in an extensive panel of Bacillus subtilis strains, including wild-type stains and mutants which: i) lack protective components such as the spore coat and its pigment(s) or the DNA protective α/β-type small acid-soluble spore proteins (SASP); ii) have an elevated spore core water content; or iii) lack enzymes involved in DNA-repair, including homologous recombination and non homologous end joining (HR and NHEJ), apurinic/apyrimidinic endonucleases, nucleotide- and base excision repair (NER & BER), translesion synthesis (TLS) by Y-family DNA polymerases and spore photoproduct (SP) removal by SP lyase (SPL). The most important factors in spore blue-light resistance were determined to be: spore coats/pigmentation, α/β-type SASP, NER, BER, TLS and SP repair. However, repair of DNA double-stand breaks by HR or NHEJ and the spore core water content had only minor roles in spore blue-light resistance. A major conclusion from this work is that blue-light kills spores by DNA damage, and the results in this work indicate at least some of the specific DNA damage. It appears that high intensity blue-light in combination with oxygen could be a significant addition to the agents used to kill bacterial spores in applied settings.