Transformation of Low Concentrations of 3-Chlorobenzoate by Pseudomonas sp. Strain B13: Kinetics and Residual Concentrations

Abstract

The transformation of 3-chlorobenzoate (3CB) and acetate at initial concentrations in the wide range of 10 nM to 16 mM was studied in batch experiments with Pseudomonas sp. strain B13. Transformation rates of 3CB at millimolar concentrations could be described by Michaelis-Menten kinetics (K(infm), 0.13 mM; V(infmax), 24 nmol (middot) mg of protein(sup-1) (middot) min(sup-1)). Experiments with nanomolar and low micromolar concentrations of 3CB indicated the possible existence of two different transformation systems for 3CB. The first transformation system operated above 1 (mu)M 3CB, with an apparent threshold concentration of 0.50 (plusmn) 0.11 (mu)M. A second transformation system operated below 1 (mu)M 3CB and showed first-order kinetics (rate constant, 0.076 liter (middot) g of protein(sup-1) (middot) min(sup-1)), with no threshold concentration in the nanomolar range. A residual substrate concentration, as has been reported for some other Pseudomonas strains, could not be detected for 3CB (detection limit, 1.0 nM) in batch incubations with Pseudomonas sp. strain B13. The addition of various concentrations of acetate as a second, easily degradable substrate neither affected the transformation kinetics of 3CB nor induced a detectable residual substrate concentration. Acetate alone also showed no residual concentration (detection limit, 0.5 nM). The results presented indicate that the concentration limits for substrate conversion obtained by extrapolation from kinetic data at higher substrate concentrations may underestimate the true conversion capacity of a microbial culture.