Studies on degradation characteristics of pyrethroid insecticides by one mixed strain and its synergistic effect

【Objective】 The study aimed to prepare the efficient mixed strain,and to provide promising candidate biological agents for controlling pyrethroid-contaminated environments.【Method】 The mixed strain were composed upon two isolated strains Bacillus cereus ZH-3 and Streptomyces aureus HP-S-01.The optimal growth and degradation conditions were determined through single-factor experiments.The degradation ability of the mixed strain was evaluated with high performance liquid chromatography(HPLC).【Result】 The optimal conditions for growth and biodegradation were obtained as follows:inoculum biomass 0.4 g/L,temperature 28 ℃,pH 7.5,and with shaking speed 150 r/min.Under these conditions,the mixed strain effectively degraded cypermethrin(50 mg/L) with a degradation rate up to 90% within 72 h.Furthermore,the mixed strain tolerated and efficiently degraded high concentrations of cypermethrin(100-500 mg/L) with a degradation rate up to 80% within 72 h.The optimal inoculating rate was 1∶1 based on single strain ZH-3 and HP-S-01.At such inoculating rate,the degradation rates for cypermethrin,fenvalerate and bifenthrin were 91.6%,92.5% and 95.7%,respectively.The degradation efficiency was significantly enhanced compared with the single strain.【Conclusion】 The mixed strain may have synergistic effect on degradation of cypermethrin,fenvalerate and bifenthrin.