|Other Abstract||~Beta-cypermethrin(beta-cyp), also known as Cyano(3-phenoxyphenyl)methyl 3-(2,2-dichloroethenyl)-2,2-dimethylcyclopropanecarboxylate and cyano ether valerate, is an agricultural insecticide widely used for the prevention and control of aphids, thrips, cotton aphids and other pests in agriculture. It is easily soluble in organic solvents. However, with the extensive use of pyrethroid pesticides, pesticide residues have become a hot topic of concern, and biodegradation is considered to be an effective way to degrade pesticides. The degradation of beta-cypermethrin by lactic acid bacteria was studied in this paper.
With 335 strains of lactic acid bacteria isolated from whole corn silage as the research object, a strain (numbered 3-27) that could effectively degrade beta-cypermethrin was found after screening. Morphological observation and staining showed that the strain was Gram-positive. The 16S rRNA gene sequence of strain 3-27 was further analyzed by BLAST homology. Finally, strain 3-27 was identified as Lactobacillus pentosus. In this paper, the degradation of beta-cypermethrin by Lactobacillus and its application in the degradation of pesticide residues in silage were reported for the first time. The research results are as follows.
1. Strain 3-27 could degrade beta-cypermethrin in a large pH range, and the strain showed the strongest degradation ability at pH 7.0 after 72 h culture. Within the temperature range of 20℃–40℃, the strain could degrade beta-cypermethrin within the temperature range of 30℃–40℃, and the degradation ability increased with the temperature, and reached the highest at 40℃. The strain tolerated substrates at concentrations ranging from 50 mg/L to 200 mg/L and was not degraded at 250 mg/L. The addition of nutrients such as glucose, peptone, and yeast extract to the mineral salt medium could enhance the degradation of the substrate by the strain. When the strain was cultured for 24 h, the degradation rate in the medium with yeast extract was 52%, which was higher than that in other groups with or without yeast extract. The degradation of beta-cypermethrin by strain 3-27 increased with the increase of inoculation amount of the strain, and reached 94% at 96 h.
2. The degradation of beta-cypermethrin in alfalfa silage for different days was studied by strain 3-27. The results showed that the degradation of beta-cypermethrin in alfalfa silage increased gradually with the prolongation of fermentation days, and decreased slightly after 90 days of fermentation. During the silage process, the degradation of beta-cypermethrin in the non-inoculated control group was also changed along with the variation of fermentation days. The degradation rate of beta-cypermethrin in the 30% inoculated treatment was always the highest among the 30% and 40% dry matter and reached the highest at 60 days, 57.23%. Compared with the control without pesticide, the dry matter content of fresh alfalfa samples with different dry matter was not affected by pesticide addition, but the non-protein nitrogen content was decreased. At the same time, in 30% dry matter, the crude protein content of pesticide treatment group was significantly higher than that of control group (P <0.001). The chemical composition and fermentation quality of alfalfa silage were tested for 90 days. The results showed that the dry matter content in the addition group of strain 3-27 was higher than that in the non-addition group and the ammonia nitrogen content was lower than that in the control group at two different dry matter levels. Among them, propionic acid content was significantly reduced in the 30% dry matter inoculation group (P <0.05), while lactic acid and acetic acid showed no significant changes. The lactic acid and WSC contents were increased in the 40% dry matter inoculation group.
3. In this study, the microbial diversity in alfalfa samples was studied by real-time quantitative monomolecule sequencing. The results showed that the microbial diversity of fresh alfalfa samples was higher than that of silage alfalfa. The number of Firmicutes and Proteobacteria was significantly higher than that of other phyla at the level and genus level. In the control of 30% DM alfalfa silage fermented for 3 days, it was mainly composed of Enterococcus (31.79%), Pediococcus (30.59%), Lactobacillus (18.03%), Enterobacter (12.18%) and Lactococcus (3.76%). With the prolongation of fermentation days, the relative abundance of Enterococcus was firstly decreased and then increased, and the relative abundance of Pediococcus was the dominant microorganism, and the relative abundance at 7, 14, 30, 60 and 90 days were 43.61%, 82.68%, 79.47%, 74.76% and 68.08%, respectively. In silage inoculated with 30%DM of Lactobacillus pentosus, the relative abundance of Lactobacillus varied from 46.83% to 95.55% during silage, followed by other genera (1.97%) and Pediococcus (1.73%). In 40% DM alfalfa silage, the relative abundance of more than 1% in 40% dry matter alfalfa was in the genera Pediococcus (43.61%), Enterococcus (12.64%), Lactobacillus (12.15%), Lactococcus (11.13%), Panbacteria (8.16%), Enterobacter (5.33%) and Weissella (1.79%).|