TRANSFORMATION OF LOW CONCENTRATIONS OF 3-CHLOROBENZOATE BY PSEUDOMONAS SP STRAIN B13 - KINETICS AND RESIDUAL CONCENTRATIONS

The transformation of 3-chlorobenzoate (3CB) and acetate at initial co ncentrations in the wide range of 10 nM to 16 mM was studied in batch experiments with Pseudomonas sp, strain B13, Transformation rates of 3 CB at millimolar concentrations could be described by Michaelis-Menten kinetics (K-m, 0.13 mM; V-max, 24 nmol . mg of protein(-1). min(-1)). Experiments with nanomolar and low micromolar concentrations of 3CB i ndicated the possible existence of two different transformation system s for 3CB, The first transformation system operated above 1 mu M 3CB, with an apparent threshold concentration of 0.50 +/- 0.11 mu M. A seco nd transformation system operated below 1 mu M 3CB and showed first-or der kinetics (rate constant, 0.076 liter . g of protein(-1). min(-1)), with no threshold concentration in the nanomolar range, A residual su bstrate concentration, as has been reported for some other Pseudomonas strains, could not be detected for 3CB (detection limit, 1.0 nM) in b atch incubations with Pseudomonas sp, strain B13, The addition of vari ous concentrations of acetate as a second, easily degradable substrate neither affected the transformation kinetics of 3CB nor induced a det ectable residual substrate concentration, Acetate alone also showed no residual concentration (detection limit, 0.5 nM). The results present ed indicate that the concentration limits for substrate conversion obt ained by extrapolation from kinetic data at higher substrate concentra tions may underestimate the true conversion capacity of a microbial cu lture.