BIODEGRADATION OF METHYL-PARATHION BY BACTERIA ISOLATED OF AGRICULTURAL SOIL

Resumen

A methyl-parathion degrading consortium of bacteria was isolated from agricultural soils in central Mexico (Morelos state), using methyl-parathion as the only carbon source. The ability of the consortium to degrade methyl-parathion, was assessed with a mineral medium containing 15 mg/L of pesticide; remnants concentration of methyl-parathion were measured by gas chromatography Different colonies were chosen from the consortium obtained, depending on their color, growth shape, morphology, consistency, borders and surface. As much as eleven different genera of bacteria were found in the consortium, which were tested for enzymatic activity by measuring change in absorbance at 410 nm, when a 15 mg/L solution of methyl-parathion was exposed to an extract containing the enzyme (a phosphotriesterase), to produce dimethylthiophosphoric acid and p-nitrophenol. From the eleven tested species plus Flavobacterium sp. ATCC 27551 strain, only five of them showed phosphotriesterase activity on the methyl-parathion. Because most of the isolated bacteria are pathogens it becomes difficult to establish recommendations towards the extensive use of one of these strains in natural environments. However, these bacteria could be considered as a potential source of enzymes to reduce environmental contamination by methyl-parathion and its residues.