The Virulence Plasmid-Encoded impCAB Operon Enhances Survival and Induced Mutagenesis in Shigella flexneriafter Exposure to UV Radiation

摘要

Upon exposure to UV radiation, Shigella flexneri SA100 displayed survival and mutation frequencies comparable to those ofEscherichia coli AB1157, which contains a functional UmuDC error-prone DNA repair system. Survival of SA100 after UV irradiation was associated with the presence of the 220-kb virulence plasmid, pVP. This plasmid encodes homologues of ImpA and ImpB, which comprise an error-prone DNA repair system encoded on plasmid TP110 that was initially identified in Salmonella typhimurium, and ImpC, encoded upstream of ImpA and ImpB. Although the impBgene was present in representatives of all four species ofShigella, not all isolates tested contained the gene.Shigella isolates that lacked impB were more sensitive to UV radiation than isolates that containedimpB. The nucleotide sequence of a 2.4-kb DNA fragment containing the imp operon from S. flexneri SA100 pVP was 96% identical to the impoperon from the plasmid TP110. An SA100 derivative with a mutation in the impB gene had reduced survival following UV irradiation and less UV-induced mutagenesis relative to the parental strain. We also found that S. flexneri contained a chromosomally encoded umuDC operon; however, theumuDC promoter was not induced by exposure to UV radiation. This suggests that the imp operon but not theumuDC operon contributes to survival and induced mutagenesis in S. flexneri following exposure to UV radiation.