CONJUGATIVE TRANSFER OF R-PLASMIDS BETWEEN ESCHERICHIA-COLI STRAINS ON SALINE SELECTIVE MEDIA AND IN SEAWATER

The conjugative transfer of two R plasmids (RP4 and pRAB15) in seawater and in saline culture media has been studied using different mating methods on solid or in liquid media. The direct mating on the medium used for the selection of transconjugants (mating-selection medium) yielded more reliable results. However, this method was only applicable when donor and recipient cells survived long enough for transfer and plasmid expression to occur. In addition, results showed that the transfer of plasmids RP4 and pRAB15 was possible, at frequencies ranging from 10(-4) to 10(-9), in saline media either prepared with seawater or supplemented with NaCl, and occurred at very low frequency (2.1 x 10(-10), for pRAB15 only) in seawater, when donor and recipient cells were previously grown on saline medium.