The Degradation Of Hexaconazole By Sphingobacterium Multivorum And Ensifer Adhaerens

Hexaconazole is a triazole fungicide widely used in China.It has the characteristics of broad-spectrum and high-efficiency and is mainly used for controlling rice sheath blight,wheat powdery mildew and tomato gray mold.Hexaconazole is stable and difficult to degrade in environment and has developmental toxicity and potential carcinogenicity.Therefore the existence of hexaconazole poses a certain risk to the environment.The Sphingobacterium multivorum B-3 and Ensifer adhaerens E-3 with high effective degradation of hexaconazole were screened in the laboratory.In the early stage,the degradation characteristics and pathways of Sphingobacterium multivorum B-3 have been studied.The Ensifer adhaerens E-3 is a newly screened hexaconazole-degrading bacterium.Therefore,this study is based on Sphingobacterium multivorum B-3 and Ensifer adhaerens E-3.The degradation mechanism and simulation application in soil of Sphingobacterium multivorum B-3,the degradation characteristics of hexaconazole by Ensifer adhaerens E-3 were studied.These studies provide a theoretical basis for bioremediation of hexaconazole.The specific conclusions are as follows:(1)The whole genome of Sphingobacterium multivorum B-3 was sequenced by de novo sequencing.The results showed that the genome contained 5523 genes and the total length of the gene is 5394999 bp,which is 88.26% of genome.The GC content of the gene region is 41.11%.Then the genes were annotated with NR,COG,GO and KEGG.The genome was used as a reference genome for transcriptome analysis.(2)The transcriptome sequencing of Sphingobacterium multivorum B-3 between hexaconazole-treated and solvent control was conducted by RNA-sequencing.The results showed that there were 864 differential genes between the hexaconazole-treated and solvent control group,of which 337 were up-regulated and 527 were down-regulated.GO analysis showed that the differential genes mainly focus on catalytic activity,binding proteins,metabolic processes and membrane part.KEGG analysis showed that the differential genes are mainly related to metabolism,most of which are related to carbohydrate metabolism,energy metabolism and amino acid metabolism.Then through in-depth exploration of the differential genes,the expression of aldehyde dehydrogenase and monooxygenase was significantly up-regulated in hexaconazole-treated group.Hexaconazole can be oxidized to 2-(2,4-dichlorophenyl)-1-(1H-1,2,4-triazol-1-yl)hexane-2,5-diol by Sphingobacterium multivorum B-3,which may be due to the participation of monooxygenase.Meanwhile the RND transporters and ABC transporters involved in metabolism and detoxification of toxic substances were also up-regulated.These genes may be related to the degradation of hexaconazole.(3)The degradation of hexaconazole in soil by Sphingobacterium multivorum B-3 was studied.The result showed that soil microorganisms have a great effect on the degradation of hexaconazole.The addition of Sphingobacterium multivorum B-3 can synergize with microorganisms in soil to promote the degradation of hexaconazole.The half-life of hexaconazole in the natural soil and the natural soil containing degradation strain is 138.6 d and 77.0 d,respectively.The half-life of hexaconazole in the sterilized soil containing degradation strain is 346.5 d.While in the absence of degradation strain,the hexaconazole was essentially not degraded in the sterilized soil.(4)An Ensifer adhaerens strain with degradation activity of hexaconazole was obtained during the culture of Sphingobacterium multivorum B-3,which is a nitrogen-fixing and rhizosphere bacterium promoting growth of plants.The degradation conditions of hexaconazole by Ensifer adhaerens E-3 were optimized.The results showed that Ensifer adhaerens E-3 has the highest degradation rate of hexaconazole at temperature of 30 °C,pH of 6.0,initial inoculum of 0.2 g/L and initial concentration of hexaconazole of 50 mg/L.The degradation rare is 74.7% in 7 d and the half-life is 3.6 d.