Photodynamic effects of dyes on bacteria: IV. Lethal effects of acridine orange and 460- or 500-nm monochromatic light in strain of Escherichia coli that differ in repair capability

Abstract

• Lethal effects of acridine orange (AO) and monochromatic 460- or 500-nm light were measured in strains of Escherichia coli that differ in repair capability. Strains WP10 ( recA) and B s-1 ( lexA uvrB) were more sensitive by factors of 17 to 281 (based on F 37 values) than the strian which tested the most resistant in the presence of AO at both wavelengths, WP2s ( uvrA). The difference in sensitivity between the reA and WP2s strains was greater with AO and 500-nm light (281-fold) than with 460-nm light (115-fold) suggesting that although DNA lesions produced by either 460-nm or 500-nm light in the presence of AO are rendered non-lethal by rec + lex + -dependent repair processes, such repair is more efficient for the lesions produced by 500-nm light. • Survival curves with AO and 460-nm light were either of the simple exponential type (WP2 and B s−1) or were exponential with a small (WP10) or moderate (WP2s) shoulder. In contrast, the survival curves with AO and 500-nm light were of the 2-component typ for the 4 strains tested. The resistant component made up 7–75% of the population. The distinctly different survival-curve shapes obtained at the 2 wavelenghts indicate that difference DNA lesions are produced by AO and 460- and 500-nm light. The data obtained for lethality with AO and 500-nm and light are consistent with result previously reported, which indicate that the very high mutation rates obtained with recA strains are the consequence of the absence of rec + and lex + repair of DNA lesions.