R plasmids which alter ultraviolet light-sensitivity and enhance ultraviolet light-induced mutability in Pseudomonas aeruginosa.

R plasmids pMG1, R2, R931 and pMG15 increased the survival of Pseudomonas aeruginosa exposed to ultraviolet radiation (u.v.) in the wild type, and uvr and polA mutants but did not alter the u.v.-response of a recA mutant. The R plasmid RPL11 reduced u.v.-survival in the wild type, and uvr and polA mutants but did not alter the u.v.-response of a recA host. All the plasmids enhanced the level of spontaneous and u.v.-induced back mutation (Trp+) in a trpB1 strain. The effect of sublethal concentration of sodium arsenite following u.v.-irradiation was examined. It was concluded that in strains trpB1(pMG1) and trpB1(R931), u.v.-protection is determined by a recA+-dependent, arsenite-sensitive repair pathway, whereas in strains trpB1(R2) and trpB1(pMG15), u.v.-protection is determined by a recA+-dependent, arsenite-insensitive step in DNA repair.