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While it seems likely that the ability to induce the expression of recA-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 Escherichia coli are either unstable or simply do not express the UV-resistance-mutagenesis phenotype in Pseudomonas aeruginosa. 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 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 while 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 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.

F116 is a temperate-generalized transducing phage of Pseudomonas aeruginosa. Genetic evidence leads to the conclusion that F116 prophage DNA is maintained extrachromosomally as a plasmid. Preliminary physical evidence is presented to support this hypothesis.

A suppressor of the mutations which inhibit the establishment of lysogeny in Pseudomonas aeruginosa has been found to be encoded by P. aeruginosa plasmids of four separate incompatibility groups. The wide distribution of this phenotype (designated Sly for suppressor of lysogeny establishment deficiency) indicates that these plasmids are able to enhance or replace host functions involved in the stable establishment of extrachromosomal DNA.

Recent concern over the release of genetically engineered organisms has resulted in a need for information about the potential for gene transfer in the environment. In this study, the conjugal transfer in Pseudomonas aeruginosa of the plasmids R68.45 and FP5 was demonstrated in the freshwater environment of Fort Loudoun Resevoir, Knoxville, Tenn. When genetically well defined plasmid donor and recipient strains were introduced into test chambers suspended in Fort Loudoun Lake, transfer of both plasmids was observed. Conjugation occurred in both the presence and absence of the natural microbial community. The number of transconjugants recovered was lower when the natural community was present. Transfer of the broad-host-range plasmid R68.45 to organisms other than the introduced recipient was not observed in these chambers but was observed in laboratory simulations when an organism isolated from lakewater was used as the recipient strain. Although the plasmids transferred in laboratory studies were genetically and physically stable, a significant number of transconjugants recovered from the field trials contained deletions and other genetic rearrangements, suggesting that factors which increase gene instability are operating in the environment. The potential for conjugal transfer of genetic material must be considered in evaluating the release of any genetically engineered microorganism into a freshwater environment.

Transduction of Pseudomonas aeruginosa plasmid Rms149 by the generalized transducing bacteriophage phi DS1 was shown to occur during a 9-day incubation of environmental test chambers in a freshwater reservoir. Plasmid DNA was transferred from a nonlysogenic plasmid donor to a phi DS1 lysogen of P. aeruginosa that served both as the source of the transducing phage and as the recipient of the plasmid DNA. When the concentration of donors introduced into the chambers was varied while the recipient concentration in each chamber was at a level equivalent to natural concentrations of P. aeruginosa, the concentration of plasmid-containing donor cells introduced was shown to affect the frequency of transduction significantly. Transduction was observed both in the absence and in the presence of the natural microbial community. The presence of the natural community resulted in a rapid decrease in the numbers of the introduced donors and recipients and a decrease in the number of transductants recovered. These results demonstrate the potential for naturally occurring transduction in aquatic environments and indicate that donor load may be an important parameter in assessing this potential.