The Role Of Gut Bacteria In The Process Of Infection By Beauveria Bassiana

Dendroctonus valens Le Conte（Red Turpentine Beetle,RTB）is a highly destructive invasive pest in Chinese forestry,which origins in North America.In China,it mainly attacks pine plants.and since its broken,has destroyed over ten thousands ha of pine stands.Therefore,the development of effective biological control is one of the best way to solve the problem of RTB at present.Beauveria bassiana,a multi-host and widely-distributed fungus in nature,induce continuous infectivity to varieties of insects,which is one of the most widely studied insect pathogen fungi in the biological control system.In addition,as an important tissue of insects,the gut is inhabited by a large number of microorganisms,insect gut bacteria play a vital role in the host’s health.However,it is not clear whether the gut bacteria of RTB is involved in resist pathogen strains.This study mainly uses a axenic RTB larvae,Miseq sequencing,fungal infection and other technical methods to assess whether RTB gut bacteria participate in host resistance to foreign pathogenic fungi,and analyzes the effects of Beauveria Bassiana on the diversity and structure of RTB gut bacteria.It further analyzes the key bacteria of RTB infected by Beauveria Bassiana,and the interaction between key bacteria and pathogenic fungi.Main research results concludes as below:1.Clarify the gut bacteria in synergistic with Beauveria Bassiana to kill RTBChoose Beauveria bassiana Bb093 isolated from RTB and RTB 3^nd instar ofDendroctonus valens with or without gut bacteria for infection analysis.Beauveria bassiana concentration of 1×10³spores/m L,1×10⁴spores/m L,1×10⁵spores/m L and 1×10⁷spores/m L.The half lethal time of no-anxenic and anxenic RTB were 5.90±0.34d/8.73±0.09d、5.86±0.33d/7.61±0.37d、4.67±0.26d/6.25±0.66d、3.64±0.88d/5,45±0.16d,respectively.The results of bioassay under different concentrations of infection showed that the death rate of RTB with gut bacteria was significantly higher.2.Beauveria Bassiana significantly affect the RTB gut bacterial population,resulting in a significant increase in the relative abundance of Erwinia sp.In 16 representative gut samples of RTB,we finally obtained 572,692 sequences,and according to the principle that 97%of the sequence similarity of 16S r RNA gene is the same operational taxon（OTU）,a total of 260 OTUs were obtained.To observe the effect of Beauveria bassiana on gut bacteria of the larva of RTB from the perspective of OTUs.A total of 15 phylum,26 class,60 order,99 family,160 genera and 192 species were identified based on OTU taxonomic status.Option 1 x 10⁷spores/m L Beauveria infection RTB four days later,on the intestinal floradiversity analysis found that:after infected by Beauveria bassiana,RTB change of gut bacteria,the invasion of pathogenic fungi causing RTB reduced intestinal fungus species diversity,and species composition change.The infection of a pathogenic fungus with lymphadenus resulted in the disorder of intestinal flora.In addition,the proportion of Erwinia sp.was 94.06±3.78%,which was significantly increased.3.Clear Erwinia sp.can accelerate the death of RTB with Beauveria Bassiana infected In order to verify the role of Erwinia sp.in host RTB resistance to fungal invasion,the intestinal strain B306 of RTB was fed back to the sterile RTB intestinal tract and infected with 1×10⁷ spores/m L Beauveria bassiana.It was found that the half-lethal time of the two groups inoculated with Bb093 after aseptic RTB inoculation and Bb093 after aseptic RTB inoculation was 8.35±0.12d/6.17±0.73d respectively.The results showed that the red fat-size intestinal bacteria,Erwinia sp.,and pathogenic fungi worked together to accelerate the death of RTB.