Bacterial diversity in the soybean rhizosphere and the application potential in Xinjiang, China

To explore the diversity and plant growth-promoting (PGP) traits of culturable rhizosphere bacteria in soybean fields across different planting regions of Xinjiang, we collected rhizosphere soil samples from three representative soybean planting areas along latitudinal gradients (high, middle, and low latitudes). We isolated a total of 81 bacterial strains and purified them from these samples using the dilution spread plate and streak plate methods. Molecular identification and phylogenetic analysis of the obtained strains were performed based on 16S rRNA gene sequence analysis, and evaluated their functional characteristics including nitrogen fixation, phosphate solubilization, and potassium release. The results showed that the isolates were phylogenetically classified into 9 genera, 9 families, 6 orders, 5 classes, and 3 phyla, with Sinorhizobium and Microbacterium as the dominant genera. The Shannon diversity index and Pielou evenness index of culturable soybean rhizosphere bacteria in the low-latitude region were 1.56 and 0.97, respectively, both higher than those in the mid-latitude region (0.54 and 0.49) and the high-latitude region (0.90 and 0.82), despite the smaller total number of culturable strains in this region. A total of 57 nitrogen-fixing strains, 1 phosphorus-solubilizing strain and 3 potassium-solubilizing strains were isolated. Among them, 2 beneficial bacteria with multiple PGP functions were identified, namely Acinetobacter sp. strain A11 and Arthrobacter sp. strain BP7. Five potential novel species of the genus Microbacterium were preliminarily identified. In conclusion, our results revealed the diversity, distribution characteristics and application potential of beneficial bacteria in the soybean rhizosphere of Xinjiang, providing core strain resources for the establishment of microbial strain resource libraries in arid regions of Northwest China.