Summary: While it seems likely that the ability to induce the expression of -controlled genes is nearly universal among the eubacteria, the expression of plasmid-borne ultraviolet (UV)-resistance and mutagenesis genes seems to be species-dependent in a complex fashion. Some plasmids encoding UV-resistance and mutagenesis functions only express these phenotypes in a select number of bacterial species. Several UV-resistance plasmids that express these functions in are either unstable or simply do not express the UV-resistance-mutagenesis phenotype in . In order to clarify the role of these plasmids in microbial ecology, we have undertaken a study of the ability of the well-characterized UV-resistance IncN plasmids pKM101 and R46 to express the UV-resistance phenotype in . In addition, we have examined the IncP plasmids RP4 and R68.45, observed to confer a UV-resistant phenotype upon , for the ability to express this phenotype in . Our experiments reveal that while pKM101 and R46 transfer to 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 . Studies of plasmids R68.45 and RP4 in revealed that they do not express UV-resistance functions in this species. UV-resistance plasmids may play an important role in the natural ecology of bacterial habitats exposed to solar radiation or to various DNA-damaging natural and man-made chemicals.


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