A kinetic study of chlorinated solvent cometabolic biodegradation by propane-grown Rhodococcus sp. PB1

An aerobic bacterial strain, named PB1, was microbiologically characterized and subjected to assays of cometabolic biodegradation of chlorinated aliphatic hydrocarbons (CAHs) aimed at (i) investigating its capacity to biodegrade vinyl chloride (VC), cis-1,2-dichloroethylene (cis-DCE), 1,1,2-trichloroethane (1,1,2-TCA), chloroform (CF) and 1,1,2,2-tetrachloroethane (1,1,2,2-TeCA); and (ii) evaluating the suitability of a kinetic model with inhibition and transformation product toxicity to describe CAH biodegradation by PB1. The strain proved to be closely related to the genus Rhodococcus. It biodegraded VC, cis-DCE, 1,1,2-TCA and CF via aerobic cometabolism on propane, but not 1,1,2,2-TeCA. CAH biodegradation by PB1 was satisfactorily described by the tested kinetic model. The maximum-specific biodegradation rates were in the 1–11 μmol/(mgprotein day) range. The transformation capacities varied from 0.6 to 3 μmol/mgprotein. Propane exerted a significant inhibition on both CF and cis-DCE biodegradation. CF, at 52 μM, did not inhibit propane utilization. An analysis of different inhibition models showed that cis-DCE inhibition on propane utilization was satisfactorily simulated with the competitive model, with an inhibition constant equal to 70% of the cis-DCE half-saturation constant. A final assay specifically aimed at validating the kinetic model and verifying the estimates of the kinetic parameters yielded a satisfactory result. The results provide positive indications on the feasibility of utilizing strain PB1 for CAH biodegradation in aquifers and wastewaters.