Cytotoxicity associated with trichloroethylene oxidation in Burkholderia cepacia G4

The effects of trichloroethylene (TCE) oxidation on toluene 2-monooxygenase activity, general respiratory activity, and cell culturability mere examin ed in the toluene-oxidizing bacterium Burkholderia cepacia G4. Nonspecific damage outpaced inactivation of toluene 2-monooxygenase in B. cepacia G4 ce lls. Cells that had degraded approximately 0.5 mu mol of TCE (mg of cells(- 1)) lost 95% of their acetate-dependent O-2 uptake activity (a measure of g eneral respiratory activity), yet toluene-dependent O-2 uptake activity dec reased only 35%. Cell culturability also decreased upon TCE oxidation; howe ver, the extent of loss varied greatly (up to 3 orders of magnitude) with t he method of assessment. Addition of catalase or sodium pyruvate to the sur faces of agar plates increased enumeration of TCE-injured cells by as much as 100-fold, indicating that the TCE injured cells were ultrasensitive to o xidative stress. Cell suspensions that had oxidized TCE recovered the abili ty to grow in liquid minimal medium containing lactate or phenol, but recov ery was delayed substantially when TCE degradation approached 0.5 mu mol (m g of cells(-1)) or 66% of the cells' transformation capacity for TCE at the cell density utilized, Furthermore, among B. cepacia G4 cells isolated on Luria-Bertani agar plates from cultures that had degraded approximately 0.5 mu mol of TCE (mg of cells(-1)), up to 90% mere Tol(-) variants, no longer capable of TCE degradation. These results indicate that a toxicity thresho ld for TCE oxidation exists in B. cepacia G4 and that once a cell suspensio n has exceeded this toxicity threshold, the likelihood of reestablishing an active, TCE-degrading biomass from the cells will decrease significantly.