Cometabolic decomposition of trichloroethylene by recombinant hydroxyquinol 1,2-dioxygenase

Abstract

Trichloroethylene (TCE) is known to microbially decomposed by a cometabolic process. In this study, a dioxygenase for the ring cleavage of benzenetriols was used to catalyze the cometabolic oxidation of TCE. Hydroxyquinol 1,2-dioxygenase (HQD) was obtained in vitro using a recombinant technique, and its catalytic function and products in the TCE cometabolic transformation were identified. The HQD (CphA-I) was cloned from Pseudarthrobacter chlorophenolicus A6, overexpressed, and purified using Ni2+-nitrilotriacetic acid (Ni2+-NTA) affinity chromatography, and soluble form of enzymes with 34 kDa protein size were effectively achieved with a high expression rate (4,177 μg/mL). TCE was effectively decomposed by CphA-I, and the specific activity was 5.1 U/mg-protein. The Hill equation was found to describe well the kinetics of TCE decomposition by CphA-I, which were determined as: vmax = 1.06 mM/min, KM = 1.44 mM, and nH = 2.41. This indicates that CphA-I has at least three cooperative binding sites for TCE decomposition, further accentuating the high affinity between the enzyme and the substrate. Glyoxylate and chloral hydrate were identified as the primary decomposition products from TCE cometabolic oxidation. This suggested that CphA-I exhibited a cometabolism catalytic function similar to those of methane monooxygenase and toluene dioxygenase. These results are expected to provide fundamental information for the enzymatic remediation of organic contaminants.