Prevalence of Pseudomonas aeruginosa FP plasmids which enhance spontaneous and UV-induced mutagenesis

From work reported here and from previous studies 16 out of 53 (30%) FP plasmids (i.e. those plasmids that promote host chromosome transfer) of Pseudomonas aeruginosa are found to protect host cells against UV irradiation. 13 of these UV-protecting FP plasmids were tested to determine their mode of DNA repair and were found to contribute to error-prone repair because of their enhancement of UV-induced mutagenesis and in most instances spontaneous mutagenesis as well. Some of these plasmids were tested for their behaviour in a DNA polymerase I deficient (Pol^-) mutant of P. aeruginosa; the remainder could not be tested due to plasmid instability in the Pol^- mutant. 11 of these FP plasmids provided wild-type level of UV protection to the mutant. 4 of the plasmids tested (FP18, FP103, FP109 and FP111) were able to enhance the mutant's ability to host cell reactivate UV irradiated phage, though not to the level of the Pol⁺ parent. The presence of FP18 or FP111 in the Pol^- mutant did not increase polymerase I-like enzymatic activity. It is concluded that the plasmids do not confer a polymerase activity functionally equivalent to host DNA polymerase I. It is possible however, that the plasmids code for another polymerase or for a cofactor which interacts with a host polymerase, as seen by the partial restoration by FP plasmids of host-cell reactivation of UV-irradiated phage in the polymerase I deficient mutant. The mutagenic properties of those FP plasmids tested appears to be nonspecific because of their ability to mutate two host chromosomal genes, trpB1 and leu38 and an R plasmid gene, bla. The implications of the prevalence of FP plasmids in P. aeruginosa which enhance mutagenesis are discussed.