Studies On Ginseng Seed Microbiome And Endophytic Antagonistic Bacteria RZP58

Ginseng is a genuine medicinal plant in Jilin Province,which is easy to be infected by diseases during cultivation.Ginseng root rot and rust rot are two common soil-borne diseases of ginseng.In this study,the diversity of microbial community structure in ginseng seed shell and seed embryo were analyzed by high throughput sequencing.A biocontrol endophytic bacterium RZP58 with high antagonistic effect against ginseng root rot and rust rot was isolated and screened from seed embryos.It was identified as Bacillus velezensis.The composition of its medium and fermentation conditions were optimized,and the chemotropism response of the strain to ginseng root exudates was investigated.（1）The results of high-throughput sequencing showed that there was a significant difference in the abundance distribution of microorganisms in the seed shell and seed embryo,with Protebacteria being the most dominant bacterial phylum in the ginseng seed shell and Cyanobacteria being the most dominant bacterial phylum in the ginseng seed embryo at the phylum level,and Ascomycota being the most dominant fungal phylum in both the seed shell and seed embryo.At the genus level,the most dominant bacterial genus in the ginseng seed shell was Trichococcus and the most dominant bacterial genus in the seed embryo was uncultured＿bacterium＿o＿Chloroplast;the most dominant fungal genus in the ginseng seed shell was Cercophora and the most dominant fungal genus in the seed embryo was Mortierella.Functional prediction using PICRUSt software revealed that the relative abundance of some functional metabolic genes was high in ginseng seed embryos and very low in seed shells;FUNGuild ecological functional group analysis revealed that the seeds carried fungi that might be probiotic or potential seed-borne pathogens.（2）A total of 88 bacterial strains were isolated from healthy ginseng seeds by tissue culture,including 15 strains in the seed shell and 73 strains in the seed embryo.After screening,11 strains,8 in the seed shell and 3 in the seed embryo,were found to have antagonistic effects on both root rot and rust rot of ginseng,among which 9 antagonistic strains had phosphorus solubilizing ability and 1 strain each was able to produce ferricyanin and IAA,but none had nitrogen fixing ability.RZP58 isolated from the seed embryo had the best antagonistic effect on root rot and rust rot with 82.33%and 82.67%inhibition rate.The strain was identified as Bacillus velezensis by physiological,biochemical and molecular biology.Strain RZP58 was capable of producing protease,amylase,cellulase andβ-glucanase.（3）By optimizing the composition of the culture medium and fermentation conditions through single factor and orthogonal experiments,the inhibitory effect of RZP58 sterile fermentation filtrate on ginseng root rot pathogens was improved.When the culture medium formula was 1.5%glucose,2.5%peptone,0.5%Na Cl,fermentation conditions were 36℃,p H 8,inoculation amount was 1.5%,and fermentation time was 48 hours,the obtained sterile fermentation filtrate had the best inhibitory effect on ginseng root rot pathogens.（4）The composition of culture medium and fermentation conditions were optimized by single factor and orthogonal test.The best inhibitory effect of the sterile fermentation filtrate of strain RZP58 on ginseng rust rot fungus was that the culture medium was composed of 2%sucrose,1%acid hydrolysis casein,0.5%Na Cl.When the fermentation conditions were 32℃,p H 7,inoculation amount 1.5%,and fermentation time 48 h,the sterile fermentation filtrate obtained had the best inhibitory effect on ginseng rust rot fungus.（5）Antibacterial strain RZP58 showed different degrees of chemotaxis response to 13different kinds of sugars and amino acids.When the concentration of arabinose was 0.1 mg·L^-1,the incubation time was 60min,the concentration of tryptophan was 10 mg·L^-1,the incubation time was 75 min,and the p H value was 7,the influence on the chemotaxis of RZP58 strain reached the maximum.