INHIBITION, INACTIVATION, AND RECOVERY OF AMMONIA-OXIDIZING ACTIVITY IN COMETABOLISM OF TRICHLOROETHYLENE BY NITROSOMONAS-EUROPAEA

The kinetics of the cometabolism of trichloroethylene (TCE) by the amm onia-oxidizing soil bacterium Nitrosomonas europaea in short-term (<10 -min) incubations were investigated. Three individual effects of TCE c ometabolism on this bacterium were characterized. First, we observed t hat TCE is a potent competitive inhibitor of ammonia oxidation by N. e uropaea. The K-i value for TCE (30 mu M) is similar to the K-m for amm onia (40 mu M) Second, we examined the toxicity associated with TCE co metabolism by N. europaea. Stationary-phase cells of N. europaea oxidi zed approximately 60 nmol of TCE per mg of protein before ammonia-oxid izing activity was completely inactivated by reactive intermediates ge nerated during TCE oxidation. At the TCE concentrations used in these experiments, ammonia did not provide significant protection against in activation. Third, we have determined the ability of cells to recover ammonia-oxidizing activity after exposure to TCE. Cells recovering fro m TCE inactivation were compared with cells recovering from the specif ic inactivation of ammonia-oxidizing activity by light. The recovery k inetics were indistinguishable when 40% or less of the activity was in activated. However, at increased levels of inactivation, TCE-inactivat ed cells did not recover as rapidly as light-inactivated cells. The ki netics of recovery appear to be dependent on both the extent of inacti vation of ammonia-oxidizing activity and the degree of specificity of the inactivating treatment.