Study On The Degradation Of Neonicotinoid Pesticides By Microorganisms During The Fermentation Of Bee Bread

The main route of exposure to pesticide residues in honey bees in the hive is dietary intake.The fermentation of bee pollen in the hive to form bee bread involves complex microbial metabolism and biochemical reactions,which have significant degradation effects on antibiotic residues as well as a variety of nutrients.The group’s preliminary study found significant degradation of neonicotinoid pesticide residues during the fermentation of bee bread.It has not been reported.Therefore,in this thesis,five neonicotinoid insecticides were used to study the microbial degradation of pesticide residues in bee bread during fermentation,to clarify the dominant strains of bee bread that degrade pesticide residues in the test,and to provide a theoretical basis for revealing the degradation mechanism of pesticide residues by microorganisms during the formation of honey bee food.The main research results are as follows:1.Degradation of neonicotinoid insecticides by microorganisms during the fermentation of bee breadMicroorganisms in bee bread at different fermentation times were cultured with the LuriaBertani medium to study the degradation of five neonicotinoid insecticides,namely dinotefuran,thiamethoxam,clothianidin,imidacloprid and acetamiprid.The results showed that there were significant differences in the degradation of the test pesticide residues by microorganisms in bee bread at different fermentation times,among which the degradation of dinotefuran by bee bread suspensions in the 7th and 9th day was significant,reaching18.7% and 24.6% for 50 μg/L dinotefuran,17.2% and 16.8% for 500 μg/L dinotefuran,respectively,and 500 μg/L dinotefuran and 18.1% and 23.2% respectively.2.Microbial diversity analysis of bee bread at different fermentation timesThe microbial diversity of bee bread at different fermentation times was analyzed by 16 S r DNA high-throughput sequencing to explore the relationship between the structure and abundance of bee bread microflora and the degradation of neonicotinoid pesticides.The results showed that there were some differences in the abundance of bee bread microflora at different levels of fermentation time.The abundance of bee bread microflora was relatively high in the 7th day.The abundance of Lactobacillus and Bacillus,as the dominant groups in bee bread,belonged to the Phylum Firmicutes with relatively high abundance in the 7th and9 th day.The microbial abundance of bee bread showed a trend of increasing and then decreasing with the increase of fermentation time,which was similar to the trend of the degradation rate of dinotefuran in the above experiment.3.Study on the dominant dinotefuran degrading bacteria during the fermentation of bee breadA dominant strain of dinotefuran degrading microorganisms was isolated and screened by pure microbial culture technique in the 7th day of bee bread.The degradation rates of 50,500 and 1000 μg/L dinotefuran reached 32.6%,25.6% and 19.1%,respectively.The physiological and biochemical characteristics and 16 S r DNA gene sequence identified as Lysinibacillus sp.,named BB-7,which is a Gram-positive bacterium with yellowish,round or oval colony,with an uneven edge,smooth surface and slightly raised middle.4.Study on the influencing factors of microbial degradation of dinotefuran in the fermentation process of bee breadThe main factors influencing the microbial degradation of pesticide residues during the fermentation of bee bread were investigated by studying the effect of different p H,Na Cl concentrations and temperature on the degradation of dinotefuran by the dominant bacterium BB-7.The results showed that the dominant bacterium BB-7 grew fastest at 30°C,p H 7 and Na Cl concentration of 10 g/L,and grew well in the p H range of 4.5-7.2(bee bread fermentation)and degraded up to 16.5%-25.2% of 50 μg/L dinotefuran;the Na Cl concentration during bee bread fermentation was 0.6-1.5%,and the degradation rate of 50μg/L dinotefuran by the dominant bacterium BB-7 at a Na Cl concentration of 10 g/L(1%salt concentration)was up to 32.2%;the temperature in the hive was about 34°C,and the degradation rate of 50 μg/L dinotefuran by the dominant bacterium BB-7 at a growth temperature between 30-35°C The highest degradation rate was 28.4%-38.4%.In conclusion,the degradation ability of the dominant bacterium BB-7 on dinotefuran was affected by the changes in p H(4.5-7.2),temperature(around 34°C)and Na Cl concentration(0.6-1.5%)during the fermentation of bee bread.