Degradation of chlorpyrifos by an endophytic bacterium of the Sphingomonas genus (strain HJY) isolated from Chinese chives (Allium tuberosum)

The degradation of chlorpyrifos (CP) by an endophytic bacterial strain (HJY) isolated from Chinese chives (Allium tuberosum Rottl. ex Spreng) was investigated. Strain HJY was identified as Sphingomonas sp. based on morphological, physiological, and biochemical tests and a 16S rDNA sequence analysis. Approximately 96% of 20mg L-1 CP was degraded by strain HJY over 15days in liquid minimal salts medium (MSM). The CP degradation rate could also be increased by glucose supplementation. The optimal conditions for the removal of 20mg L-1 CP by strain HJY in MSM were 2% inoculum density, pH 6.0, and 30-35 degrees C. The CP degradation rate constant and half-life were 0.2136 +/- 0.0063 d(-1) and 3.2451 +/- 0.0975 d, respectively, under these conditions, but were raised to 0.7961 +/- 0.1925 d(-1) and 0.8707 +/- 0.3079 d with 1% glucose supplementation. The detection of metabolic products and screening for degrading genes indicated that O,O-diethyl O-3,5,6-trichloropyridinol was the major degradation product from CP, while it was likely that some functional genes were undetected and the mechanism responsible for CP degradation by strain HJY remained unknown. Strain HJY is potentially useful for the reduction of CP residues in Chinese chives and may be used for the in situ phytoremediation of CP.