Isolation & Characterization Of Fipronil Degrading Strain R-2 And Its Degrading Characteristics

Fipronil, a new phenyl pyrazole insecticide, was produced by Rhone-Poulenc Agrochemicals Company in 1987. Because of its novel structure, unique mechanism, and high activity, fipronil has been known as one of the new generation of high-tech pesticides, and it has been widely used and applied. Fipronil is difficult to be degraded under natural conditions. Fipronil residues in natural will cause great harm to aquatic biomass and bees. The contamination of fipronil brings not only the economic losses, but also the ecological damage. Microbial activity has been proved to be the most influential and significant factor for the fipronil removal and biotransformation. Microbial remediation has been thought to be the most potential method to clean up the pesticides contamination. In this dersertation, the isolation of a strain capable of degrading fipronil, and the fipronil degrading characteristics was studied extensively.A bacterial strain of strain R-2, capable of degrading fipronil, was isolated from a fipronil-contaminated soil. Strain R-2 was preliminarily identified as Paracoccus sp. based on its physiological, biochemical characters, and the 16S rRNA gene sequence analysis.The optimal pH value for the growth of strain R-2 was 5.0-7.0, and the optimal pH was 7.0. The optimal temperature was 30℃. The optimal C/N was 8:1. Strain R-2 could utilize fipronil as sole carbon resource for growth. There was a positive correlation with the the growth and aeration. The optimal osmotic pressure for strain R-2 was 5-20 g·L-1 (NaCl). The optimal carbon and nitrogen sources for the growth of strain R-2 were glucose and organic nitrogen, respectively.The effect of environmental factors (temperature, pH value, inoculum size, cultural time, and addition of alternative nutritions) on the degradation of fipronil by strain R-2 was studied. It was found that above 85% of 50 mg·L-1 fipronil was degraded by strain R-2 within 3 d. The optimal pH value and temperature for the degradation of fipronil were 7.0 and 30℃, respectively. The degrading rate showed a positive correlation with the amount of initial inoculum size while a negative correlation with the initial concentration of fipronil. The addition of alternative glucose, peptone, or yeast extract could promote the degradation of fipronil. The addition of Zn2+and Fe3+(0.1 mmol·L-1) promoted the bacterial growth and the degradation of fipronil. However, the Ni2+, Co2+, Hg2+, and Mg2+(0.1 mmol·L-1) inhibited the degradation.When strain R-2 was inoculated into the fipronil-contaminated soil sample, the degradation of fipronil occurred mainly in the first 5 days. In the natural soil sample, the degradation of fipronil was higher than the sterilized soils. Strain R-2 could cooperate well with the indigenous microorganisms to metabolize fipronil in the soil. The degradation of fipronil was affected by the inoculum size of strain R-2, soil temperature, soil pH value, and soil moisture capacity. When strain R-2 was inoculated at 1.0×107 CFU-g-1 dry soil, the degradation of 100 mg·kg-1 fipronil by strain R-2 in soil at pH 6.0-7.0 and 30 ℃ was 75%.