Transfer of plasmid RP4 from Escherichia coli K-12 to indigenous bacteria of seawater.

Transfer of plasmid RP4 from Escherichia coli K-12 donor strain to bacteria isolated from seawater was shown to occur on filters and in sterile seawater incubated at 24 degrees C. Ten of 12 seawater isolates tested were recipient active for RP4 when the plasmid transfers were assessed by filter matings. When matings were performed in sterile seawater, seven of the 12 isolates received RP4. In sterile seawater, the transfer of RP4 from E. coli to pseudomonads was more efficient than transfer between E. coli strains. Transfer of RP4 to indigenous seawater bacteria was shown to take place both on filters and in seawater amended with Luria Bertani broth. No transconjugants were found in experiments with unamended seawater, but in experiments with amended seawater 10(-7)-10(-6) transconjugants per recipient were found. In filter matings with a 100-fold-concentrated total population of indigenous seawater bacteria, the transfer efficiency of RP4 was 4 x 10(-5) per recipient. The majority of the isolated transconjugant seawater bacteria consisted of fluorescent pseudomonads, but transconjugant strains of Aeromonas hydrophila, Pseudomonas cepacia, and Enterobacter cloacae were also found. Using an auxotrophic donor strain, selection of transconjugants on selective minimal media was shown to be an efficient strategy for detection of gene transfer to indigenous bacteria of seawater.