Cometabolism of chlorinated solvents and binary chlorinated solvent mixtures using M-trichosporium OB3b PP358

The mutant methanotroph, Methylosinus trichosporium OB3b PP358, which const itutively expresses soluble methane monooxygenase (sMMO), was used to study the degradation kinetics of individual chlorinated solvents and binary sol vent mixtures. Although sMMO's broad specificity permits a wide range of ch lorinated solvents to be degraded, it creates the potential for competitive inhibition of degradation rates in mixtures because multiple chemicals are simultaneously available to the enzyme. To effectively design both ex situ and in-situ groundwater bioremediation systems using strain PP358, kinetic parameters for chlorinated solvent degradation and accurate kinetic expres sions to account for inhibition in mixtures are required. Toward this end, the degradation parameters for six prevalent chlorinated solvents and the v erification of enzyme competition model for binary mixtures were the focus of this investigation. M. trichosporium OB3b PP358 degraded trichloroethyle ne (TCE), chloroform, cis-1,2-dichloroethylene (c-DCE), trans-1,2-dichloroe thylene (t-DCE), and 1,1-dichloroethylene (1,1-DCE) rapidly, with maximum s ubstrate transformation rates of >20.8, 3.1, 9.5 24.8, and >7.5 mg/mg-day, respectively. 1,1,1-trichloroethane (TCA) was not significantly degraded. H alf-saturation coefficients ranged from 1 to greater than 10 mg/L. Competit ion experiments were carried out to observe the effect of a second solvent on degradation rates and to verify the applicability of the Monod model adj usted for competitive inhibition. Binary mixtures of 0.3->0.5 mg/L TCE with up to 5 mg/L c-DCE and up to 7 mg/L 1,1,1-TCA were studied with 20 mM of f ormate and no growth substrate. No competition was observed at any of these concentrations. Additional competition experiments, using binary mixtures of t-DCE with TCE and t-DCE with c-DCE, were conducted at higher concentrat ions (i.e., 7-18 mg/L) and enzyme competition was observed. Predictions fro m a competitive inhibition model compared well with experimental data for t hese mixtures. (C) 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 65: 100-1 07, 1999.