The solvent efflux system of Pseudomonas putida S12 is not involved in antibiotic resistance

The active efflux system contributing to the solvent tolerance of Pseudomon as putida S12 was characterized physiologically. The mutant P. putida JK1, which lacks the active efflux system, was compared with the wild-type organ ism. None of 20 known substrates of common multi-drug-resistant pumps had a stronger growth-inhibiting effect on the mutant than on the wild type. The amount of [C-14]toluene accumulating in P. putida S12 increased in the pre sence of the solvent xylene and in the presence of uncouplers. The effect o f uncouplers confirms the proton dependency of the efflux system in P. puti da S12. Other compounds, potential substrates for the solvent pump, did not affect the accumulation of [C-14]toluene. These results show that the effl ux system in P. putida S12 is specific for organic solvents and does not ex port antibiotics or other known substrates of multi-drug-resistant pumps.