Isolation,Degrading Characteristic And Bioremediation Of Metribuzin Degrading Strains

Metribuzin is one of the triazine herbicides,developed by Germany's Bayer in 1971.Because of its high efficiency and low dosage,metribuzin has been used worldwide in soy,potato,tomato,corn,sugar cane soils to control broadleaf weeds.Massive usage of metribuzin and other triazine herbicides has resulted in serious residues in the environment.In the river,drinking water,metribuzin and its metabolites were frequently detected.Metribuzin is toxic to algae,rats and fish.The studies of the degradation of metribuzin are insufficient,and the reportes are mainly concentrated in the study of the growth and the degradation characteristics.The degrading pathway and functional gene involved in the biodegradation of metribuzin hadn't been reported.By the method of enrichment,two bacterial strains capable of degrading metribuzin were isolated from soil contaminated by herbicide,designed as QCT6 and QCT10 respectively.According to morphological observation,physiological characteristics and phylogenetic analysis based on 16S rRNA gene sequence comparisons,strain QCT6 was identified as Paracoccus sp.and strain QCT10 was identified as Rhodococcus sp..Strain QCT6 is aerobic,Gram-stain negative,pale yellow,globular bacterium(diameter,0.9-1.1?m)without flagella.The investigation of the biological characteristics showed that the optimal growth conditions for strain QCT6 were 30 ?,0-3%NaCl,pH 7.0.Stain QCT10 is aerobic,pink,short-rod bacterium(1.1×1.2 ?m × 1.6×1.7 ?m)without flagella.The investigation of the biological characteristics showed that the optimal growth conditions for strain QCT10 were 30 ?,0-2%NaCl,pH 7.0.The degradation characteristics experiments of strain QCT6 showed that under the condition of 30 ?,with 7.5%inoculum volume,QCT6 could degrade 80%of 50 mg·L-1 metribuzin within 7 d.The optimal degradation temperature and pH value for strain QCT6 were 30 ? and 7.0.Under the condition of 30 ?,with 7.5%inoculum volume,strain QCT10 could degrade 75%of 50 mg·L-1 metribuzin within 7 d.The optimal degradation temperature and pH value for strain QCT10 were 30 ? and 7.0.The metabolic pathway of metribuzin degraded by strains QCT6 and QCT10 was analysed.Results of GC-MS analysis indicate that molecula-ion peak of 213.92 is metribuzin and molecula-ion peak of 199.96 is the metabolic product,which indicated that the metabolic product is deamination metribuzin.The bioremediation of metribuzin contaminated soil by inoculating QCT6 and QCT10 were studied under laboratory conditions.When strain QCT6 was inoculated with 1011 CFU·g-1 dry soil at the concentration of 15 mg·kg-1 metribuzin at 30 ?,metribuzin-degradation rate was 67.9%.Strain QCT6 could degrade over 60%of metribuzin at 30 ?,concentration range from 5 mg·kg-1 to 20 mg·kg-1.When the concentration was 50 mg·kg-1,degradation rate of metribuzin by QCT6 was less than 30%.When strain QCT10 was inoculated with 1011 CFU·g-1 dry soil at the concentration of 15 mg·kg-1 metribuzin at 30 ?,metribuzin-degradation rate was up to 56.1%.Strain QCT10 could degrade over 50%of metribuzin at 30 ?,concentration range from 5 mg·L-1 to 15 mg·kg-1.