Effect of organic solvents on the yield of solvent-tolerant Pseudomonas putida S12

\Solvent-tolerant microorganisms are useful in biotransformations with whol e cells in two-phase solvent-water systems. The results presented here desc ribe the effects that organic solvents have on the growth of these organism s. The maximal growth rate of Pseudomonas putida S12, 0.8 h(-1), was not af fected by toluene in batch cultures, but in chemostat cultures the solvent decreased the maximal growth rate by nearly 50%. Toluene, ethylbenzene, pro pylbenzene, xylene, hexane, and cyclohexane reduced the biomass yield, and this effect depended on the concentration of the solvent in the bacterial m embrane and not on its chemical structure. The dose response to solvents in terms of yield was linear up to an approximately 200 mM concentration of s olvent in the bacterial membrane, both in the wild type and in a mutant lac king an active efflux system for toluene. Above this critical concentration the yield of the wild type remained constant at 0.2 g of protein/g of gluc ose with increasing concentrations of toluene. The reduction of the yield i n the presence of solvents is due to a maintenance higher by a factor of th ree or four as well as to a decrease of the maximum growth yield by 33%. Th erefore, energy-consuming adaptation processes as,well as the uncoupling ef fect of the solvents reduce the yield of the tolerant cells.