LETHAL EFFECTS OF NATURAL SOLAR ULTRAVIOLET RADIATION IN REPAIR PROFICIENT AND REPAIR DEFICIENT STRAINS OF ESCHERICHIA COLI: ACTIONS AND INTERACTIONS

Abstract— The inactivation of repair proficient ( Escherichia coli K12 AB 1157, E. coli B/r) and repair deficient ( E. coli K12 AB 1886 uvrA , AB 2463 recA and AB 2480 uvrA recA ) strains of bacteria by noon sunlight has been measured. The use of biological dosimetry based on an ultraviolet (UV) sensitive strain of Bacillus subtilis spores has allowed a quantitative comparison of bacterial inactivation by solar, 254 and 302 nm radiations. Our analysis indicates that: (1) uvrA and recA gene products are involved in repair of a substantial portion of the solar DNA damage, (2) 302 nm is a more appropriate wavelength than 254 nm to represent the DNA-damaging action of sunlight and that (3) repair proficient strains are inactivated by sunlight more rapidly than expected from the levels of DNA damage induced. When populations of repair proficient bacteria are exposed to noon sunlight for 20 min, they become sensitive to the lethal action of far-UV (254 nm), MMS (0.1 M ) and to a lesser extent, mild heat (52°C).