Comprehensive Characterization of a Novel Bradyrhizobium Isolate TS001 from Indigenous Soil Microbiota in Harbin: Broad pH Adaptability, Salt Stress Tolerance, Symbiotic Nodulation, and Genetic Potential for Nitrogen Fixation

Developing elite rhizobial resources capable of surviving under extreme environmental conditions (high salinity, acidity, and alkalinity) while maintaining high nitrogen-fixing efficiency is a core objective in sustainable agriculture. This study systematically evaluated the physiological, ecological, and symbiotic characteristics of a novel indigenous soybean-nodulating strain, "TS001," isolated from soybean root nodules. A series of experiments were conducted from October 2025 to May 2026 at the Soybean Research Institute Laboratory, College of Agriculture, Northeast Agricultural University. Partial 16S rDNA sequence analysis revealed that strain TS001 shares high similarity (96.07–98.35%) with Bradyrhizobium japonicum and B. diazoefficiens, confirming its phylogenetic position within the genus Bradyrhizobium. Physiological characterization demonstrated that TS001 tolerates a broad pH range (5.0–9.0) and grows well under high NaCl concentrations (up to 2.5%); even under salt stress, its growth rate declined significantly less than that of the reference strain, indicating strong environmental resilience. In pot inoculation experiments, TS001 induced abundant nodule formation on soybean roots, with nodule dry weights comparable to those of the reference strain HH103, confirming its effective symbiotic nodulation capacity. Furthermore, PCR-based molecular detection confirmed the stable presence of symbiosis- and nitrogen fixation-specific genes, including nodA and nifH, providing genetic evidence for its nitrogen-fixing potential. Collectively, these findings demonstrate that TS001 is a promising indigenous rhizobial resource that maintains robust growth, symbiotic nodulation, and nitrogen-fixing genetic potential under typical extreme environmental conditions in the Harbin region, offering significant application prospects for smart agriculture and sustainable soybean cultivation.