Effect of Three Chlorinated Ethenes on Growth Rates for a Methanotrophic Mixed Culture

Abstract

The presence of chlorinated aliphatic hydrocarbons (CAHs) was found to decrease the net growth rate of a methanotrophic mixed culture expressing particulate methane monooxygenase (pMMO). Growth rates in the absence of CAHs were 1.48, 1.14, and 0.45 day-1 on 460, 46, and 9.3 μg/L methane, respectively. Weighted nonlinear least squares fitting of the Monod model with decay yielded best estimates (±95% confidence intervals) of 2.67 ± 0.08 μg of methane (μg of cells)-1 day-1 for the maximum methane utilization rate, 15.6 ± 1.2 μg of methane/L for the methane half-saturation coefficient, and 0.20 ± 0.05 day-1 for the endogenous respiration rate. Using this single set of kinetic parameter values, the model fit captured both the shape and the spacing of methane depletion curves covering 4 orders of magnitude in initial biomass concentration and 2 orders of magnitude in methane concentration. Growth rates on 460 μg/L methane were reduced by approximately 20% in the presence of 0.05 mg/L 1,1-dichloroethylene (1,1-DCE), 1 mg/L trans-1,2-dichloroethylene (t-DCE), or 1 mg/L trichloroethylene (TCE). A model for the effect of CAHs on growth rate was fitted to growth rate data by nonlinear least squares analysis. Competitive inhibition ap peared the important factor for the reduction in growth rates with TCE and t-DCE, and transformation product toxicity was most significant for 1,1-DCE. Finally, an inoculum expressing sMMO showed an extreme toxicity in the presence of 0.005 mg/L 1,1-DCE, but not when the inoculum expressed pMMO.