INCN PLASMIDS MEDIATE UV RESISTANCE AND ERROR-PRONE REPAIR IN PSEUDOMONAS-AERUGINOSA PAO

While it seems likely that the ability to induce the expression of rec A-controlled genes is nearly universal among the eubacteria, the expre ssion of plasmid-borne ultraviolet (UV)-resistance and mutagenesis gen es seems to be species-dependent in a complex fashion. Some plasmids e ncoding UV-resistance and mutagenesis functions only express these phe notypes in a select number of bacterial species. Several UV-resistance plasmids that express these functions in Escherichia coli are either unstable or simply do not express the UV-resistance-mutagenesis phenot ype in Pseudomonas aeruginosa. In order to clarify the role of these p lasmids in microbial ecology, we have undertaken a study of the abilit y of the well-characterized UV-resistance IncN plasmids pKM101 and R46 to express the UV-resistance phenotype in P. aeruginosa. In addition, we have examined the IncP plasmids RP4 and R68.45, observed to confer a UV-resistant phenotype upon Myxococcus xanthus, for the ability to express this phenotype in P. aeruginosa. Our experiments reveal that w hile pKM101 and R46 transfer to P. aeruginosa at a very low frequency, these plasmids, once transferred, are maintained and clearly support the expression of the UV-resistance and mutagenesis phenotype observed in E. coli. Studies of plasmids R68.45 and RP4 in P. aeruginosa revea led that they do not express UV-resistance functions in this species. UV-resistance plasmids may play an important role in the natural ecolo gy of bacterial habitats exposed to solar radiation or to various DNA- damaging natural and man-made chemicals.