Remediation of 3,5,6-Trichloro-2-Pyridinol Polluted Soil With Ralstonia sp. T6 and Construction of a Chlorpyrifos-Mineralizing Engineered Strain

TCP is a kind of metabolic product of degradation of chlorpyrifos. Ralstonia sp. T6, a TCP (3,5,6-trichloro-2-pyridinol) degrading strain of bacteria, was used in an experiment to explore its TCP degrading characteristics in soil. Results show that T6 degraded 80% of 50 mg·kg^-1 TCP in 6 days. Temperature, inoculation rate and initial concentration of the substrate were factors affecting its degrading efficiency. The optimum temperature for T6 degrading TCP was 30℃; in soils lower than 10×10⁸ CFU/kg in bacteria content, TCP biodegradation rate rose with rising bacteria content, while in soils higher than that, the rate did not rise, but fall instead with rising bacteria content. A methyl parathion hydrolase gene (mpd) from Stenotrophomonas sp. DSP-1 was inserted into 16S rDNA of Ralstonia sp. T6 by conjugation and a genetically engineered T6-mpd that is supposed to be able to completely mineralize chlorpyrifos was obtained. Culturing tests show that T6-mpd and Ralstonia sp. T6 displayed similar growth characteristics. Chlorpyrifos degrading tests show that in LB medium, the chlorpyrifos hydrolysis efficiency of T6-mpd was basically the same as that of Stenotrophomonas sp. DSP-1, but in inorganic salt medium, T6-mpd‘s 50 mg·L^-1 chlorpyrifos hydrolysis rate in 60 h reached only 36%, significantly lower than DSP-1’s. Simulated in-situ soil remediation shows that T6-mpd, 10×10⁸ CFU·kg^-1 in content, could degrade 64% of 50 mg·kg^-1 chlorpyrifos. It is, therefore, believed that Strain T6-mpd is a promising tool for bioremediation of chlorpyrifos-contaminated environment.