F'-plasmid transfer from Escherichia coli to Pseudomonas fluorescens

Various F' plasmids of E. coli K-12 could be transferred into mutants of the soil strain 6.2, classified herein as a P. fluorescens biotype IV. This strain was previously found to receive Flac plasmid: ilv, leu, met, arg, and his auxotrophs were complemented by plasmids carrying isofunctional genes; trp mutants were not complemented or were very poorly complemented. The frequency of transfer was 10^-5. Subsequent transfer into other P. fluorescens recipients was of the same order of magnitude. Some transconjugants were unable to act as donors, and these did not lose the received information if subcultured on nonselective media. Use of F' plasmids helped to discriminate metabolic blocks in P. fluorescens. In particular, metA, metB, and argH mutants were so distinguished. In addition, F131 plasmid carrying the his operon and a supD mutation could partially relieve the auxotrophy of thr, ilv, and metA13 mutants, suggesting functional expression of E. coli tRNA in P. fluorescens. In P. fluorescens metA Rif(r) mutants carrying the F110 plasmid, which carried the E. coli metA gene and the E. coli rif(s) allele, sensitivity to rifampin was found to be dominant at least temporarily over resistance. This suggests interaction of E. coli and P. fluorescens subunits of RNA polymerase. his mutations were also complemented by composite P plasmids containing the his-nif region of Klebsiella pneumoniae (plasmids FN68 and RP41). nif expression could be detected by acetylene reduction in some his⁺ transconjugants. The frequency of transfer of these P plasmids was 5 x 10^-4.