ABSTRACT
AIMS: Isolation and identification of bacteria capable of degrading organophosphate pesticide quinalphos and elucidation of its biodegradative pathway. METHODS AND RESULTS: A bacterium capable of degrading organophosphate pesticides was isolated from the pesticide-contaminated soil samples by selective enrichment on quinalphos (QP) as a sole source of carbon and energy. The bacterial strain was identified as Ochrobactrum sp. strain HZM on the basis of its morphological and biochemical characteristics and by phylogenetic analysis based on 16S rRNA gene sequences. The organism utilized various organophosphate pesticides such as quinalphos, profenofos, parathion-methyl and chlorpyrifos as growth substrates. Response surface methodology (RSM) showed optimum conditions for quinalphos degradation at pH 7 and 27°C. 2-Hydroxyquinoxaline and diethyl phosphate were identified as metabolites of quinalphos degradation by HPLC and GC-MS analysis. Cell-free extract of Ochrobactrum sp. strain HZM grown on quinalphos contained the quinalphos hydrolase activity. CONCLUSIONS: A bacterial strain capable of degrading quinalphos was isolated and identified as Ochrobactrum sp. strain HZM. The organism utilized organophosphate pesticides quinalphos, profenofos, parathion-methyl and chlorpyrifos as carbon sources. The organism degraded quinalphos by hydrolysis to yield 2-hydroxyquinoxaline and diethyl phosphate which were further utilized as carbon sources. SIGNIFICANCE AND IMPACT OF THE STUDY: The isolated bacterium Ochrobactrum sp. strain HZM was versatile in degrading various organophosphate pesticides. There was complete mineralization of quinalphos by Ochrobactrum sp. This strain could potentially be useful in the bioremediation of soil and water contaminated with toxic organophosphate pesticides.
