Enhancement of UV survival, UV- and MMS-mutability, precise excision of Tn 10 and complementation of umuC by plasmids of different incompatibility groups

Abstract

29 conjugative resistance and colicin plasmids from 19 different incompatibility (Inc) groups were examined for their ability to enhance post-ultraviolet (UV) survival and UV- and methyl methanesulfonate(MMS)-induced mutability in Salmonella typhimurium LT2 strains. 14 Muc + plasmids enhanced each of the survival and mutation-related properties tested, while 14 Muc − plasmids showed no enhancing effects in any tests. One Muc + plasmid, pRG1251 (IncH1), enhanced post-UV survival and each of the mutation-related properties tested, except MMS-induced mutagenesis. Two further noteworthy plasmids, R391 (IncJ) and R394 (IncT), produced apparent strain-dependent effects in S. typhimurium which differed from those reported to have been found in Escherichia coli. Plasmid R391 enhanced post-UV survival in S. typhimurium, in contrast to its UV-sensitizing effects in E. coli. In both hosts plasmid R391 enhanced UV- and MMS-induced mutagenesis. Plasmid R394 had no enhancing effects on UV survival or UV- and MMS-induced mutagenesis in S. typhimurium, in contrast to its reported enhancement of MMS-induced mutagenesis in E. coli. Conjugal transfer of R394 to E. coli strain AB1157 and assays of mutagenesis-related traits supported results observed in S. typhimurium. Muc + plasmids were found to enhance the frequency of precise excision of the transposom Tn 10 when inserted within hisG or trpA in S. typhimurium strains. Precise excision could be further enhanced in S. typhimurium by UV-irradiation. Analysis of Tn 10 mutants with altered IS 10 ends indicated that intact inverted repeats at the ends of Tn 10 were required for efficient enhancement of precise excision.