The toxic effects of degrading the chlorinated hydrocarbons trichloroethylene (TCE), chloroform (CF) and cis-1,2-dichloroethylene (cis-1,2-DCE) were studied in the bacterium Nitrosomonas europaea. N europaea is an ammonia-oxidizing bacterium that obtains all of its energy from the oxidation of ammonia to nitrite. This metabolic process involves two enzymes, ammonia monooxygenase (AMO) and hydroxylamine oxidoreductase (HAO). AMO has a broad substrate range and is also capable of oxidizing TCE, CF, and cis-1,2-DCE. Effects of degrading these chlorinated compounds on both AMO and HAO were studied. Cells were inactivated with known inhibitors of both AMO (light) and HAO (hydrogen peroxide) to provide comparison studies. Oxidation of the three chlorinated hydrocarbons did not always result in similar toxic effects to the cells. Whole cell studies indicated that oxidation of TCE and CF resulted in a loss of both NH������- and N���H���- dependent 0��� uptake rates, while in vitro studies indicated that at lower concentrations of both TCE (���0.05 mM) and CF (���0.10 mM) neither AMO or HAO appear to be the primary sites of inactivation. The oxidation of cis-1,2-DCE appeared to specifically inactivate AMO both in in vivo and in vitro assays. N europaea cells were also pretreated with the AMO inhibitor acetylene and incubated with the chlorinated hydrocarbons. Results of both whole cell 0��� uptake rates and the in vitro HAO assay confirms the hypothesis that the chlorinated hydrocarbons must be turned over in order to produce a toxic effect in N. europaea cells. / Graduation date: 1999