Assimilation of cis-1,2-dichloroethene by aerobic 1,4-dioxane-metabolizing bacterium Pseudonocardia dioxanivorans...

cis-1,2-Dichloroethene (cDCE) has been reported to be not only a toxic groundwater pollutant, but also an inhibitor during the biodegradation of 1,4-dioxane (DX), another emerging contaminant, and the two commonly co-occur at solvent-impacted sites. Pseudonocardia dioxanivorans CB1190 is an aerobic bacterium capable of metabolizing DX. Here, we investigated whether it can also degrade cDCE, thus overcoming the inhibitory effects . Batch culture experiments were conducted for both biodegradation kinetics and metabolomic analyses. Our results showed that CB1190 was able to degrade multiple cycles of ∼1500 μg/L cDCE as its sole substrate. This continuous degradation occurred whether the cells were grown previously on DX or glucose, implying a monooxygenase-independent reaction. Fitting of cDCE degradation data by resting cells of DX-grown CB1190 to the Michaelis-Menten model revealed a V_max of 18.6 µg/min/mg total Lowry protein and a K_m value of 1334 µg/L. For metabolomic analysis, CB1190 was grown on [U-¹³C]-labeled glucose before transitioning to reagent (unlabeled) cDCE, and the labeled carbons in the glycolysis and tricarboxylic acid cycle intermediates, as well as in the amino acids, were monitored over time. Positive unlabeling of many metabolites revealed that CB1190 indeed incorporated cDCE in cellular metabolites. Lastly, enzyme inhibition experiments and molecular docking suggested that there are two possible pathways, using cytochrome P450 or haloacid dehalogenase, via which CB1190 may degrade cDCE. These results will be valuable in changing the landscape of bioremediation of cDCE- and DX-impacted waters, especially with the synergy of CB1190 being able to use both compounds for carbon and energy, even at environmentally relevant concentrations, mitigating the need for addition of primary substrates.