Artificial and solar UV radiation induces strand breaks and cyclobutane pyrimidine dimers in Bacillus subtilis spore DNA

The loss of stratospheric ozone and the accompanying increase in solar UV f lux have led to concerns regarding decreases in global microbial productivi ty. Central to understanding this process is determining the types and amou nts of DNA damage in microbes caused by solar UV irradiation, While UV irra diation of dormant Bacillus subtilis endospores results mainly in formation of the "spore photoproduct" 5-thyminyl-5,6-dihydrothymine, genetic evidenc e indicates that an additional DNA photoproduct(s) may be formed in spores exposed to solar W-B and W-A radiation (Y. Xue and W. L. Nicholson, Appl, E nviron. Microbiol. 62:2221-2227, 1996), We examined the occurrence of doubl e-strand breaks, single-strand breaks, cyclobutane pyrimidine dimers, and a purinic-apyrimidinic sites in spore DNA under several UV irradiation condit ions by using enzymatic probes and neutral or alkaline agarose gel electrop horesis, DNA from spores irradiated with artificial 254-nm UV-C radiation a ccumulated single-strand breaks, double-strand breaks, and cyclobutane pyri midine dimers, while DNA from spores exposed to artificial W-B radiation (w avelengths, 290 to 310 nm) accumulated only cyclobutane pyrimidine dimers, DNA from spores exposed to full-spectrum sunlight (UV-B and UV-A radiation) accumulated single-strand breaks, double-strand breaks, and cyclobutane py rimidine dimers, whereas DNA. from spores exposed to sunlight from which th e W-B component had been removed with a filter ("UV-A sunlight") accumulate d only single-strand breaks and double-strand breaks, Apurinic-apyrimidinic sites were not detected in spore DNA under any of the irradiation conditio ns used. Our data indicate that there is a complex spectrum of W photoprodu cts in DNA of bacterial spores exposed to solar W irradiation in the enviro nment.