Comparative mutagenesis and interaction between near-ultraviolet (313- to 405-nm) and far-ultraviolet (254-nm) radiation in Escherichia coli strains with differing repair capabilities

Comparative mutagenesis and possible synergistic interaction between broad-spectrum (313- to 405-nm) near-ultraviolet (black light bulb [BLB]) radiation and 254-nm radiation were studied in Escherichia coli strains WP2 (wild type), WP2s (uvrA), WP10 (recA), WP6 (polA), WP6s (polA uvrA), WP100 (uvrA recA), and WP5 (lexA). With BLB radiation, strains WP2s and WP6s demonstrated a high level of mutagenesis, whereas strains WP2, WP5, WP6, WP10, and WP100 did not demonstrate significant mutagenesis. In contrast, 254-nm radiation was mutagenic in strains WP2, WP2s, WP6, and WP6s, but strains WP5, WP10, and WP100 were not significantly mutated. The absence of mutagenesis by BLB radiation in lexA and recA strains WP10, WP5, and WP100 suggests that lex+ rec+ repair may play a major role in mutagenesis by both BLB and 254-nm radiation. The hypothesis that BLB radiation selectively inhibits rec+ lex+ repair was tested by sequential BLB-254-nm radiation. With strain WP2, a fluence of 30 J/m2 at 254 nm induced trp+ revertants at a frequency of 15 X 10(-6). However, when 10(5) J/m2 or more of BLB radiation preceded the 254-nm exposure, no trp+ revertants could be detected. A similar inhibition of 254-nm mutagenesis was observed with strain WP6 (polA). However, strains WP2s (uvrA) and wP6s (polA uvrA) showed enhanced 254-nm mutagenesis when a prior exposure to BLB radiation was given.