Identification and Growth-Promoting Traits of Bacillus Species within the Bacterial Community Structure Isolated From Saline–Alkali Soil Based on High-Throughput Analysis

Salt-alkali soil severely affects plant growth and sustainable development of agriculture, some special microorganism of saline–alkali soils can improve the adaptability to adversity. However, the identification and functional exploration of these microorganisms in saline–alkali soils remain limited. Based on the integration of high-throughput sequencing with traditional microbial isolation techniques, the bacterial community structure, functional bacterial prediction, screening and growth-promoting traits were executed in mildly (SMI), moderately (SMO), and severely (SSE) saline-alkali soils in Western Jilin Province. The results indicated that soil pH, electrical conductivity, and Na+ levels were increased significantly with the salinity increase (P < 0.05), whereas the content of organic matter, and available phosphorus were significantly decreased (P < 0.05). 16 S sequencing results indicated that the abundance of the functional microbial Bacillus species were significantly more abundant in SMO than in SMI or SSE (P < 0.01), with concentrations 0.41% and 0.45% higher than in mildly and severely saline-alkali soils, respectively. Based on these findings, three Bacillus strains exhibiting excellent salt tolerance and growth-promoting traits were screened and identified from saline-alkali soils. The growth-promoting potential of Priestia megaterium and Priestia aryabhattai showed significant potential, with indole-3-acetic acid secretion levels reaching 15.17 µg/mL and 13.81 µg/mL, respectively. Bacillus subtilis exhibited the highest inorganic phosphorus solubilization capacity, with a phosphorus-solubilizing zone diameter/colony diameter ratio of 3.22. In summary, this study significantly improved the efficiency of discovering functional microorganisms from extreme environments. The functional strains obtained lay the foundation for enriching the microbial resource pool in saline-alkali soils and for the preparation of microbial inoculants. pH, AP, and SAR are the dominant factors influencing bacterial community structure. The abundance of Bacillus species were significantly higher in moderately than that in mildly or severely saline-alkali soils. Three salt-tolerant plant-promoting microorganisms were screened: Bacillus subtilis, Priestia megaterium, Priestia aryabhattai.