The Potential Mechanism Of Colonization-resistance Of Bacteria Inside Nematode To Biocontrol Bacteria

In the previous study,it was found that Bacillus nematocida B16 can kill pine wood nematode,and it can be used as biological control bacteria for pine wood nematodes.We found that some endophytes isolated form Bursaphelenchus xylophilus intestine can inhibit the growth of Bacillus nematocida B16,prevent Bacillus nematocida B16 to kill the pine nematode.The SCO41 strain is the most obvious one that inhibits the Bacillus nematocida B16.Finding the mechanism of colonization-resistance of the SCO41 against Bacillus nematocida B16 can improve the killing effect of Bacillus nematocida B16 on pine wood nematodes through some biological methods,and provide a foundation for the development and using of Bacillus nematocida B16.In this study,multiple biological methods were used to study the interaction between the SCO41 and the Bacillus nematocida B16.The results of this study are as follows.(1)Five endophytic bacteria were successfully isolated,purified and screened from the intestinal tract of pine wood nematodes.They were named SCO1,SCO2,SCO6,SCO9 and SCO41.(2)The interactions between endophytic bacterias and Bacillus nematocida B16 was studied.It was found that the SCO1 strain and the SCO6 strain had no effects on Bacillus nematocida B16 growth inhibition,but the SCO2,the SCO9 and the SCO41 can inhibit the growth of Bacillus nematocida B16,among them,the SCO41 has the strongest effect of the Bacillus nematocida B16 growth inhibition.(3)The SCO41 strain was classified and identified.The strain of SCO41 was rod-shaped,glabrous and gram-negative.The colony is smooth and round,transparent,with neat edges and sticky;it was identifieds as a new species belonging to the Phytobacter.(4)The whole genome sequence of the SCO41 strain was extracted and sequenced.Through the analysis of the sequencing results,it was found that there were 109,283 reads obtained by SCO41 strain gene sequencing,the gene size was 1,517 Mbp,the average sequence read length was 13,882 bp,the length of sequencing sequence N50 was 18,679 bp,and the average sequencing sequence quality value was 0.84.(5)Based on the analysis results of gene sequencing,the inhibition mechanism of Bacillus nematocida B16 colonization was predicted:(1)The genome of SCO41 strain contains a large number of coding genes related to flagella,but no flagella structure was found when the bacteria were morphologically identified.Therefore,it was speculated that the proteins encoded by these genes are related to the immunity of bacteria,and the proteins secreted by the strains are the main substance to inhibit the colonization of Bacillus nematocida B16.(2)Fifteen Enterobactin-related coding genes were found in the genome of the SCO41 strain.Therefore,it is speculated that Enterobactin of the SCO41 strain may be the main factor to inhibit the colonization of Bacillus nematocida B16.(3)Eleven coding genes related to HIS-I in T6 SS of VI secretory system were found in the genome annotation results of the SCO41 strain,which accounted for a large proportion of the total annotations.HIS-I in T6 SS of VI secretory system was attacked by other bacteria in the living environment of the strain and attacked by other bacteria.This may be one of the potential mechanisms for SCO41 strain to inhibit the colonization of Bacillus nematocida B16 in the intestinal tract of online worms.In conclusion,the results showed that the intestinal endophytic bacteria of nematodes had a certain effect on the immune function of nematodes,and some endophytic bacteria could reduce the effect of biocontrol bacteria on nematodes.the SCO41 strain can prevent the colonization of Bacillus nematocida B16 in the intestinal tract of pine wood nematodes,Exploring the inhibiting mechanism of SCO41 strain and Bacillus nematocida B16 at the genetic level could provide a theoretical support for the development of new biological control agents for pine wood nematode using Bacillus nematocida B16,and also our results provided a foundation to enhance the killing effect of biocontrol bacteria on nematodes through alteration of intestinal micobial structure of pine wood nematode.The innovations of this study are as that,The relationship between endophyticbacteria and biocontrol bacteria was studied,which provided support for the development of biocontrol agents by Bacillus nematocida B16 through a new idea to improve the colonization capabilities of Bacillus nematocida B16.