Biotransformation and biodegradation of methyl parathion by Brazilian bacterial strains isolated from mangrove peat

Four bacterial strains (Bacillus sp. CBMAI 1833, Bacillus cereus P5CNB, Kosakonia sp. CBMAI 1836 and Kosakonia sp. CBMAI 1835) isolated from a Brazilian mangrove peat were evaluated for biodegradation of methyl parathion. The strains Bacillus sp. CBMAI 1833 and B. cereus P5CNB showed a better methyl parathion degradation at 36 h than the Kosakonia strains. By HPLC-UV analysis, it was observed in the presence of both strains that all methyl parathion was biotransformed and biodegraded in 24 h of incubation. HPLC-ToF and GC-MS analysis were employed for identification of metabolites from the methyl parathion reactions. The first reaction of the biodegradation pathway was the direct hydrolysis of the pesticide to yield p-nitrophenol by a phase I reaction. The biotransformation of methyl parathion occurs via the nitro group reduction with the formation of an amine group in the phenolic moiety, followed by the amine acetylation to yield an acetamide derivative by phase II reactions. Further biodegradation proceeded with the hydrolysis of the acetamide product forming N-(4-hydroxyphenyl) acetamide. Bacillus sp. CBMAI 1833 and B. cereus P5CNB were also able to promote the reduction of p-nitrophenol levels in 12 days, showing potential for future bioremediation studies.