WATER-STRESS EFFECTS ON TOLUENE BIODEGRADATION BY PSEUDOMONAS-PUTIDA

We quantified the effects of matric and solute water potential on tolu ene biodegradation by Pseudomonas putida mt-2, a bacterial strain orig inally isolated from soil. Across the matric potential range of 0 to - 1.5 MPa, growth rates were maximal for P. putida at -0.25 MPa and furt her reductions in the matric potential resulted in concomitant reducti ons in growth rates. Growth rates were constant over the solute potent ial range 0 to -1.0 MPa and lower at -1.5 MPa. First order toluene dep letion rate coefficients were highest at 0.0 MPa as compared to other matric water potentials down to -1.5 MPa. Solute potentials down to -1 .5 MPa did not affect first order toluene depletion rate coefficients. Total yield (protein) and carbon utilization efficiency were not affe cted by water potential, indicating that water potentials common to te mperate soils were not sufficiently stressful to change cellular energ y requirements. We conclude that for P. putida: (1) slightly negative matric potentials facilitate faster growth rates on toluene but more n egative water potentials result in slower growth, (2) toluene utilizat ion rate per cell mass is highest without matric water stress and is u naffected by solute potential, (3) growth efficiency did not differ ac ross the range of matric water potentials 0.0 to -1.5 MPa.