Plasmid-borne catabolism of methyl parathion and p-nitrophenol in Pseudomonas sp. strain WBC-3

Pseudomonas sp. strain WBC-3 utilises methyl parathion (MP) or p-nitrophenol (PNP) as the sole source of carbon, nitrogen, and energy. A plasmid designated pZWL0 of ≈70 kb in this strain was found to be responsible for MP and PNP degradation. This was based on the fact that the plasmid-cured strains showed PNP−MP− phenotype and the PNP+MP+ phenotype could be conjugally transferred. We have also cloned a 3.4-kb HindIII fragment which exhibited methyl parathion hydrolase activity, which revealed a methyl parathion hydrolase (mph) gene whose DNA sequence is 99.5% identical to the recently identified mpd gene from Plesiomonas sp. M6 [C. Zhongli, L. Shunpeng, F. Guoping, Isolation of methyl parathion-degrading strain M6 and cloning of the methyl parathion hydrolase gene, Appl. Environ. Microbiol. 67 (2001) 4922-4925]. The mph gene was functionally expressed in Escherichia coli and the relative activities of the enzyme against different substrates were determined. The sequence alignment and phylogenetic analysis suggested that MPH and MPD evolved independently from other well-studied organophosphate hydrolases and may be originated from class B β-lactamase family. Subsequently obtained a 6.5-kb KpnI and BamHI fragment containing the above HindIII fragment revealed that the mph gene was physically located in a typical transposon.