Objective To address the issues of low sulfur availability in agricultural soils and sulfur deficiency in crops, this study is aimed to screen sulfur-oxidizing bacteria (SOB) with both high sulfur oxidation efficiency and multiple bioactivities from the rhizosphere soil of oilseed rape in Yunnan, China, and to evaluate their potential for agricultural application. Method SOB were isolated using targeted enrichment and isolation techniques. Sulfur oxidation activity was evaluated based on pH reduction and sulfate production. Isolates were screened for multifunctional PGP traits, including nitrogen fixation, zinc solubilization, and phosphate solubilization. Promising strains were further assessed for biological activities such as siderophore production, heteroauxin (IAA) secretion, and antagonism against plant pathogens. Their efficacy in promoting seed germination and Solanum lycopersicum plant growth was validated. Result A total of 313 SOB strains were isolated. Among them, 16 Strains presented strong sulfur-oxidizing capacity (sulfate production: 38.53-66.54 mg/L). Based on morphological, physiological, biochemical characteristics, and 16S rDNA sequence analysis, three high-activity strains, YNK-FB0053, YNK-FB0056, and YNK-FB0057, were identified as Burkholderia gladioli, Pantoea endophytica, and Priestia aryabhattai, respectively. All three strains possessed the activities of nitrogen fixation, zinc solubilization, phosphate solubilization, and siderophore secretion. They also harbored genes associated with antibiotic synthesis (srfAB, yndJ, ituC, sboA, bioA, NRPS, and PKSI). Seed germination tests demonstrated that these strains increased germination rates of Brassica napus L, Solanum lycopersicum, and Secale cereale by 16.67%–44.33% and total seedling length by 17.95%–33.70%. In pot experiments with Solanum lycopersicum, all three strains significantly (P<0.05) promoted plant growth, with chlorophyll content, plant height, and stem diameter increased by approximately 15%–30%, root length extended by more than 55%, and belowground biomass showing the most pronounced improvement. In terms of nutrient accumulation, total nitrogen, phosphorus, potassium, and sulfur contents were all enhanced, while iron content had the greatest increase, reaching 112.50%. Conclusion The rhizosphere soil of Yunnan oilseed rape harbors SOB strains with both high-efficiency sulfur oxidation and multiple plant growth-promoting functions. Strain YNK-FB0053 (B. gladioli), YNK-FB0056 (P. endophytica), and YNK-FB0057 (P. aryabhattai) significantly enhance seed germination, Solanum lycopersicum plant growth, and mineral element accumulation, demonstrating substantial potential for agricultural application as novel multifunctional bioinoculants.
