COMETABOLISM OF CHLORINATED SOLVENTS BY NITRIFYING BACTERIA - KINETICS, SUBSTRATE INTERACTIONS, TOXICITY EFFECTS, AND BACTERIAL RESPONSE

Pure cultures of ammonia-oxidizing bacteria, Nitrosomonas europaea, we re exposed to trichloroethylene (TCE), 1,1-dichloroethylene (1,1-DCE), chloroform (CF), 1,2-dichloroethane (1,2-DCA), or carbon tetrachlorid e (CT), in the presence of ammonia, in a quasi steady-state bioreactor . Estimates of enzyme kinetics constants, solvent inactivation constan ts, and culture recovery constants were obtained by simultaneously fit ting three model curves to experimental data using nonlinear optimizat ion techniques and an enzyme kinetics model, referred to as the inhibi tion, inactivation, and recovery (IIR) model, that accounts for inhibi tion of ammonia oxidation by the solvent, enzyme inactivation by solve nt product toxicity, and respondent synthesis of new enzyme (recovery) . Results showed relative enzyme affinities for ammonia monooxygenase (AMO) of 1,1-DCE approximate to TCE > CT > NH3 > CF > 1,2-DCA. Relativ e maximum specific substrate transformation rates were NH3 > 1,2-DCA > CF > TCE approximate to 1,1-DCE > CT (=O). The TCE, CF, and 1,1-DCE i nactivated the cells, with 1,1-DCE being about three times more potent than TCE or CF. Under the conditions of these experiments, inactivati ng injuries caused by TCE and 1,1-DCE appeared limited primarily to th e AMO enzyme, but injuries caused by CF appeared to be more generalize d. The CT was not oxidized by N. europaea while 1,2-DCA was oxidized q uite readily and showed no inactivation effects. Recovery capabilities were demonstrated with all solvents except CF. A method for estimatin g protein yield, the relationship between the transformation capacity model and the IIR model, and a condition necessary for sustainable com etabolic treatment of inactivating substrates are presented. (C) 1997 John Wiley & Sons, Inc.