HP7 Persistent Organic Pollutants (POPs)
201 Oregon Ballroom
1:20 PM - 5:20 PM, Thursday
() Lactate induction of the ammonia mono-oxygenase enzyme and solvent cometabolism.
Byl, T1, 2, Faridi, F.2, Kochary, S.2, Hampton, L.2, 1 USGS, Nashville, TN, USA2 Tennessee State University, Nashville, TN, USA
ABSTRACT- Water containing bacteria was collected from a PCE-contaminated karst aquifer in northern-central Tennessee to establish liquid, 1-liter microcosms. The microcosms were spiked with known concentrations of perchloroethylene (PCE) and 11 different formulations of lactic acid. The ammonia-lactate formulation caused a rapid removal of PCE and oxygen (O2). Similar results achieved using a second set of microcosms established with ammonia-lactate to re-test the removal rate of PCE and O2 indicated a possible co-metabolic PCE-removal process. Although only one report of PCE-cometabolism was found in the literature, we hypothesized that ammonia-oxidizing bacteria indigenous to the karst aquifer were capable of cometabolizing PCE with the ammonia mono-oxygenase (AMO) pathway. To test this hypothesis, microcosms were established using different forms of ammonia (ammonia-lactate, ammonia-chloride, ammonium plus sodium lactate), reference controls (sterile, live-no food, sodium lactate, sterile + ammonia lactate), and ammonia mono-oxygenase inhibitor (2-chloro-6-(trichloromethyl) pyridine). Microcosms treated with ammonia-lactate had the most rapid reduction of PCE and O2, followed by the ammonium + Na-lactate treatment. The other live microcosms treated with ammonia also experienced significant drops in PCE and O2 after 24 hours. The control (sterile and live-no food) microcosms did not experience a significant drop in PCE in the same time period. After 24 hours, the rapid PCE removal in all the ammonia-treated microcosms slacked off, due to the consumption of the oxygen. Tests with the AMO inhibitor did not prevent the PCE removal or O2 consumption, indicating the inhibitor did not work on this particular AMO enzyme or bacteria. It is possible that the lactate stimulates AMO or protects the enzyme from inhibition. Additional tests need to be conducted to characterize the optimum pH, stoichiometric balance, and different AMO inhibitors. None-the-less, these preliminary results provide strong evidence that karst bacteria indigenous to this aquifer can cometabolize PCE.
Key words: allosteric induction, oxygenase, perchloroethylene, cometabolism