Background and Aim: Chlorpyrifos is an organophosphate pesticide used in agriculture for pest control. It is a relatively persistent poison and an environmental pollutant with adverse effects on human health. This study was conducted to isolate and characterize chlorpyrifos-degrading bacteria from rice field soils in Amol City, Iran.

Materials and Methods: In this experimental study, soil samples were collected from rice fields with a history of toxic pollution. A minimal salt broth (Msb) medium containing 100 mg/l chlorpyrifos as the carbon and energy source was used for isolating pesticide-degrading bacteria. The colonies were characterized by Gram staining and biochemical tests and sequencing was done using the PCR method.

Results: Four chlorpyrifos-degrading bacterial strains were isolated from the soils. They included Bacillus licheniformis strain IARI-M-12, Bacillus pumilus strain MS42, Bacillus cereus strain ESB15, and Delftia tsuruhatensis strain SJ113. The effects of temperature and pH on the bacterial strains were investigated. The Bacillus strains showed the fastest growth at a temperature of 35^o C and a pH=7 in a Msb medium containing chlorpyrifos.

Conclusion: The results of this study demonstrate that bacteria in the farmland can degrade the chlorpyrifos poison. Thus, these bacteria can be used to reduce the environmental problems resulting from soil contamination with chlorpyrifos in the ecosystem.