Graduate Thesis Or Dissertation
 

Effects of substrate interactions, toxicity, and bacterial response during cometabolism of chlorinted solvents by nitrifying bacteria

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/hx11xh770

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  • Cometabolic biodegradation processes, important for bioremediation of hazardous waste sites, are not well understood and have not been modeled thoroughly. Toxic effects and bacterial responses to toxicity may change intracellular enzyme levels, rendering traditional enzyme kinetics models inappropriate. This document presents a novel cometabolic enzyme kinetics model that incorporates enzyme inhibition (caused by the presence of a cometabolic compound), inactivation (resulting from toxicity of a cometabolic product), and recovery (associated with bacterial synthesis of new enzyme). The inhibition, inactivation, and recovery (BR) model assumes that enzyme inactivation is a function of nongrowth substrate oxidation and that recovery is a function of growth substrate oxidation. Consisting of two, nonlinear, ordinary differential equations, the model is solved numerically and estimates of model parameters obtained by nonlinear optimization. Results are presented from experiments with pure cultures of ammoniaoxidizing bacteria, Nitrosomonas europaea, exposed to trichloroethylene (TCE), 1,1-dichloroethylene (1,1-DCE), chloroform (CF), 1,2-dichloroethane (1,2-DCA), or carbon tetrachloride (CT), in the presence of ammonia, in a quasi-steady-state bioreactor. Relative enzyme affmities for ammonia monooxygenase (AMO) were 1,1-DCE TCE > CT > NH3 > CF >l,2 -DCA. Relative maximum specific substrate transformation rates were NH3 > 1,2-DCA > CF > TCE r=11,1-DCE > CT (-0). TCE, CF, and 1,1-DCE inactivated the cells, with 1,1-DCE about three times more potent than TCE or CF. Inactivating injuries caused by TCE and 1,1-DCE appeared limited primarily to AMO, as indicated by undiminished functioning of other electron transport proteins, but injuries caused by CF appeared to be more generalized. TCE- and 1,1-DCE-induced inactivation was proportional to the amount of solvent oxidized. CT was not oxidized by N. europaea while 1,2-DCA was oxidized quite readily and showed no inactivation effects. Recovery capabilities were demonstrated with all solvents except CF. Demonstration of recovery capabilities indicates that sustainable cometabolic treatment of chlorinated solvents may be achievable. Managing inactivation effects to allow bacterial recovery by protein synthesis is shown to be much more favorable energetically than growth of cells. A mathematical relationship between the transformation capacity model and the IIR model is shown, and a condition necessary for sustainable cometabolic treatment of inactivating substrates is presented.
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