Optimization of methyl parathion biodegradation and detoxification by cells in suspension or immobilized on tezontle expressing the opd gene

Abstract

The goal of this study was to optimize methyl parathion (O,O-dimethyl-O-4-p-nitrophenyl phosphorothioate) degradation using a strain of Escherichia coli DH5α expressing the opd gene. Our results indicate that this strain had lower enzymatic activity compared to the Flavobacterium sp. ATCC 27551 strain from which the opd gene was derived. Both strains were assessed for their ability to degrade methyl parathion (MP) in a mineral salt medium with or without the addition of glucose either as suspended cells or immobilized on tezontle, a volcanic rock. MP was degraded by both strains with similar efficiencies, but immobilized cells degraded MP more efficiently than cells in suspension. However, the viability of E. coli cells was much higher than that of the Flavobacterium sp. We confirmed the decrease in toxicity from the treated effluents through acetylcholinesterase activity tests, indicating the potential of this method for the treatment of solutions containing MP.

Keywords:

• Organophosphate pesticides
• methyl-parathion
• opd gene
• tezontle
• biodegradation

Acknowledgments

We would like to acknowledge Dr. Andres Aguilar Negrete of the Institute of Physics, UNAM, for his help in scanning pictures with the scanning electron microscope (SEM) and Dr. Ernesto Ortiz-Sun of the Institute of Biotechnology, UNAM, for providing us with the competent cells used in this work. This work was partially funded by the grant FOMIX 93760.