Biodegradation of chlorpyrifos and 3, 5, 6-trichloro-2-pyridinol by a novel rhizobial strain Mesorhizobium sp HN3

A chlorpyrifos (CP) and 3,5,6-trichloro-2-pyridinol (TCP) degrading bacterial strain, Mesorhizobium sp. HN3, was isolated and characterized. Mesorhizobium sp. HN3 degraded CP efficiently up to 400mg/L initial concentration at wide range of temperatures (30-40 degrees C) and pH (6.0-8.0). However, optimal degradation of CP was achieved at 37 degrees C and neutral pH (7.0) at an initial inoculum density 2x10(7) colony forming unit/mL of culture medium. Kinetic parameters for CP degradation by Mesorhizobium sp. HN3 were estimated at different initial concentrations. Cultures exhibited significant variation (P0.05) in the specific growth rate (), cell mass formation rate (Q(X)) and the substrate uptake rate (Q(S)) during degradation of CP. The values of kinetic parameters increased up to 100mg/L CP and decreased at higher concentration. Investigation of degradation metabolites indicated that CP is converted to diethylthiophosphate and TCP that leads to the formation of 3,5,6-trichloro-2-methoxypyridine.