Effects of oxygen and nitrogen conditions on the transformation kinetics of 1,2-dichloroethenes by Methylosinus trichosporium OB3b and its sMMOC mutant.

Abstract

Transformation kinetics of trans- and cis-dichloroethylenes (DCE) by Methylosinus trichosporium OB3b wild type (WT) and PP319, a mutant that expresses soluble methane monooxygenase at copper levels up to micro 12 microM Cu (sMMOC), were determined to assess the effects of O2 level and N2-fixation on degradation capabilities. Two issues were examined: (1) the influence of O2 level and nitrogen-limitation on DCE degradation kinetics and toxicity in both organisms, and (2) the relative utility of PP319 for contaminant degradation in bioreactors. When both organisms were grown under high O2 conditions (80% saturation in air), maximum transformation rates (Vmax) and apparent first-order rate constants (Vmax/KM) were lower compared with organisms grown under low O2 conditions (10% saturation in air) regardless of nitrogen level. Further, Vmax values were near zero in nitrogen-limited WT cultures when O2 was high (as expected), whereas PP319 retained moderate Vmax levels even at high O2 levels. In general, elevated O2 conditions reduced DCE degradation rates in OB3b, although the negative effects of O2 were less in PP319 than in the WT. Given that PP319 retained moderate DCE degradation rates under most O2 and copper conditions, the mutant appears to have some utility for biodegradation applications.