Molecular cloning and characterization of a Methyl Parathion Hydrolase from an Organophosphorus-degrading Bacterium, Serratia marcescens MEW06.

An organophosphorus-degrading bacterium MEW06, which exhibited excellent biodegradation capabilities towards 50 mg/L of methyl parathion (MP), paraoxon and dimethoate, was isolated from Sand Lake (Wuhan, China) and identified as Serratia marcescens subsp. marcescens based on physiological-biochemical characteristics and a 16S rDNA sequence-based phylogenetic tree. MEW06 genome contains a 31.09-kDa methyl parathion hydrolase (MPH) (MPHGM004539) that was 54.9% similar to Pseudomonas sp. WBC-3's MPH. RT-qPCR revealed that mph(GM004539) gene expression was significant up-regulated when co-cultured with MP. mph(GM004539) without signal peptide (mph(GM004539)Delta sp) was successful cloned and expressed in Escherichia coli BL21 (DE3). Optimized specific enzyme activity of MPHGM004539 Delta SP was 5.26 U/mg under 35 degrees C and pH 11.0 conditions when MP as the substrate. Additionally, Co2+, Cd2+ and Fe2+ increased the enzyme activity level. MP could be degraded by MPHGM004539 Delta SP into p-nitrophenol probably by hydrolyzing the P-O ester bond. Virulence of MP towards Drosophila melanogaster W1118 was reduced by MEW06 or MPHGM004539 Delta SP biodegradation. This is the first cloning and characterization of MPH from the organophosphorus-degrading bacterium S. marcescens. MEW06 and its MPH have potential roles in the bioremediation of organophosphorus pesticide-contaminated eco-systems.