Characterization Of Rhizosphere And Root Microbiota Of Radix Astragali In Shanxi

Background: Microorganism that inhabits in the plant surface and internal has a close relationship with host,they can form a stable niche interact with each other.Roots influence the rhizosphere by altering soil pH,soil structure,oxygen availability.In addition,plant genotypes,habitats and growth years also affect the colonization of microorganisms in plants.Conversely,plant microorganisms affect plant growth,secondary metabolism and stress resistance by providing nutrients and anabolic hormones.At present,researchers have studied the microorganisms in various medicinal plants.By using traditional culture method,researchers have isolated endophytic fungi from Astragalus which can promote a variety of secondary metabolites,but root microbiota of Astragalus especially bacteria has not been reported.Objects: Using culture method and molecular ecology methods,this study intends to explore root microorganism group in Shanxi Huangqi.Through analyzing the structure of microbial in rhizosphere and root of Astragalus in different habitats,the endophytic bacteria with potential growth promoting effect were screened from fresh root.Then the characteristics of microflora in rhizosphere and root of Shanxi Huangi were clarified.We hope that the current work will provide microbiological cues for understanding quality formation of A.mongholicus in Shanxi,exploitation of microbial resources and development of microbial fertilizer and related products in the field planting of A.Mongolicus.Methods:(1)Characterization of rhizospheric microbiological communities in Astragali Mongolici Radix of Shanxi:The root rhizosphere soil as the experimental materials and non rhizosphere soil as control,using Automated ribosomal intergenic spacer analysi(ARISA)on the origin and growth period of Huangqi rhizosphere community structure characteristics;(2)Characterization of root microbiota in Shanxi Astragali Mongolici Radix: Huangqi from different genotype,producing area and planting patterns as experimental materials,using ARSIA analysis anatomical structure effects of microbial.Then using high-throughput sequencing analysis the character of microbial in the periderm;(3)Taking fresh root of Shanxi Huangqi as experimentalmaterial,the endophytic were isolated by traditional culture method,screened the strain with ACC deaminase activity using ACC as the only nitrogen,then studied its growth characteristics.Results:(1)Characterization of rhizospheric microbiological communities in Astragali Mongolici Radix of Shanxi: The soil bacterial communities were fingerprinted by automated ribosomal intergenic-spacer analysis(ARISA).Compared with bulk soil communities,the rhizospheric communities in 2-and 3-year-old herbs shifted obviously,and the community similarities were decreased but the diversities increased.Meanwhile,there was no significant difference in the community similarity between 5-year-old herbs and bulk soils and their sample rare-fraction curves were more consistent with each other.When compared to the specimens from other production areas,the communities in Shanxi had relatively lower core operational taxonomic unit(OTUs)but had significantly higher abundance of core OTUs shared by all areas.(2)Characterization of root microbiota in Shanxi Astragali Mongolici Radix:Bacterial communities residing Astragalus membranaceus and Astragalus mongholicus root parts(i.e.,the periderm and secondary vascular tissue)were first characterized by ARISA,showing that the periderm microbiota was more diverse and clearly separated by host genotype and geographical location but the microbiota in the vascular tissue was only separated by host genotype.Then microbiota residing on the surface and inside of the periderm was analyzed by pyrosequencing of 16 S rRNA amplicons.The results showed that bacterial phyla of Proteobacteria,Planctomycetes and Bacteroidetes dominated the periderm bacterial assemblages.When taken core and specific taxa into account,A.mongholicus harbored more diverse microbiomes than A.membranaceus,regardless of the geography and field practice.Among the cultivated A.mongholicus plant specimens,those growing in Shanxi colonized more distinct and diverse microbiomes.For both host genotypes,the conventional cultivation consistently exhibited a negative effect on taxonomic complexity when compared to the planting pattern “imitating wild conditions”.With focus on microbiota in Shanxi,the taxonomic species associated with the genotype,geography and planting pattern were discriminated.Taken together,the bacterial communities in the root periderm were genotype-and location-dependent and thebacterial assemblages in Shanxi were more distinct and diverse.(3)Screening of endophytic bacteria strains that contain ACC deaminase: Using culture-dependent method,a total of 56 strains of endophytic bacteria were isolated from the roots of A.mongholicus in Shanxi.Among these strains,8 from the genus of Pseudomonas were screened and contained ACC deaminase.Effects of the temperature,pH value and salt concentration on their growth were primarily examined and demonstrated that the optimum temperature and pH value were 28 ? and 7.2respectively and that the strains can grow in the medium containing up to 4% NaCl.Conclusion: Our study demonstrated that the rhizosphere and root bacterial communities in A.mongolicus of Shanxi were distinct and more complex in comparison with the other areas.And the growth year for more than 4 years increased the similarity of the bacterial communities in the rhizosphere to bulk soil.According to the phenotypic characterization of taxonomic species discriminated by deep-sequencing,the endophytic bacteria having potential growth-promoting effect were screened from A.mongholicus roots in Shanxi.