Abstract: Endophytic bacteria can promote plant growth and are important germplasm resources for biological fertilizers. Astragalus membranaceus (Fisch.) Bge. is a regional characteristic bulk product of “Top ten medicinal materials in Gansu Province”. It is of great significance to understand the structure and function of its seed endophytic bacteria for the discovery of microbial resources. In this study, microbial high-throughput sequencing technology was used to analyze the diversity of endophytic bacteria in Astragalus membranaceus seeds and predict the function of FAPROTAX. Endophytic bacteria were isolated by isolation, culture and purification technology, and their plant growth promoting (PGP) characteristics in vitro were detected. The results showed that the endophytic bacteria in Astragalus membranaceus seeds contained 2582 operational taxonomic units (OTUs), belonging to 25 phyla and 277 families, with Pseudomonadota as the dominant phylum (43.84%). The main function of the bacterial community was chemoisooxia (29.70%), and there were also a small number of potential pathogenic bacteria (15.61%). Nine kinds of endophytic bacteria were isolated from seven kinds of culture media, with Bacillus (93.75%) as the dominant genus. Among the 16 endophytic bacteria, two strains produced indole-3-acetic acid (IAA), 11 strains produced siderophores, six strains of phosphate solubilizing bacteria and 15 strains of nitrogen fixing bacteria. Our results confirmed that endophytic microorganisms in Astragalus membranaceus seeds colonize and coexist with a variety of beneficial functional bacteria and potential pathogenic bacteria, which can provide a basis for the mining and scientific utilization of endophytic microbial resources in seeds.

Key words: Astragalus membranaceus, seed, endophytic bacteria, microbial diversity, structure and function