The CAM-OCT plasmid enhances UV responses of Pseudomonas aeruginosa recA mutants

Abstract

The effect of the CAM-OCT plasmid on responses to UV irradiation of Pseudomonas aeruginosa recA mutants was characterized. Mutant alleles examined included rec-1, rec-2, and recA7::Tn501. The plasmid substantially enhanced both survival and mutagenesis of RecA- cells after treatment with UV light. Survival of the RecA-(CAM-OCT) cells after UV irradiation was intermediate between that seen in the wild-type P. aeruginosa PAO1 and the increased survival seen in PAO1(CAM-OCT) cells. Mutability was quantitated by the reversion to carbenicillin resistance of strains carrying a bla(Am) mutation on a derivative of plasmid RP1. UV-induced mutagenesis of CAM-OCT carrying recA mutants occurred at levels comparable to that seen in PAO1(CAM-OCT). The ability of CAM-OCT plasmid to suppress the recombination deficiency in recA mutants was tested by assaying for bacteriophage F116L-generalized transduction of a Tn7 insertion in the alkane utilization genes of CAM-OCT. Transduction of the Tn7 insertion was not detected in RecA-(CAM-OCT) strains but was easily seen in PAO1(CAM-OCT), indicating that the plasmid does not encode a recA analog. The results indicate that the CAM-OCT UV response genes are expressed in RecA- cells, which differs from results seen with other UV response-enhancing plasmids. The results suggest that CAM-OCT either encodes several UV responses genes itself or induces chromosomal UV response genes by an alternate mechanism.