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.