THE SPECIFIC GROWTH-RATE OF PSEUDOMONAS-PUTIDA PAW1 INFLUENCES THE CONJUGAL TRANSFER RATE OF THE TOL PLASMID

The kinetics of the conjugal transfer of a TOL plasmid were investigat ed by using Pseudomonas putida PAW1 as the donor strain and P. aerugin osa PAO 1162 as the recipient strain. Short-term batch mating experime nts were performed in a nonselective medium, while the evolution of th e different cell types was determined by selective plating techniques. The experimental data were analyzed by using a mass action model that describes plasmid transfer kinetics. This method allowed analysis of the mating experiments by a single intrinsic kinetic parameter for con jugal plasmid transfer. Further results indicated that the specific gr owth rate of the donor strain antecedent to the mating experiment had a strong impact on the measured intrinsic plasmid transfer rate coeffi cient, which ranged from 1 x 10(-14) to 5 x 10(-13) ml per cell per mi n. Preliminary analysis suggested that the transfer rates of the TOL p lasmid are large enough to maintain the TOL plasmid in a dense microbi al community without selective pressures.