Defying Salinity, Drought, and pH Extremes: A Multifunctional Rhizobacterium, Burkholderia gladioli ST3M-39a, Matches Fertilizer Efficacy in Wheat via Phosphate Solubilization

Global phosphorus scarcity and the environmental impacts of chemical fertilizers necessitate sustainable microbial alternatives for agriculture. We characterized Burkholderia gladioli ST3M-39a, a maize rhizosphere isolate, as a multifunctional plant growth-promoting rhizobacterium with exceptional climate resilience. The strain achieved rapid phosphate solubilization (177.96 ± 5.26 µg/mL within 24 h; molybdenum-antimony assay), zinc solubilization, and ammonia production, EPS production, and produced stress-alleviating enzymes (cellulase and protease). Crucially, it maintained robust growth and phosphate-mobilizing capacity under extreme abiotic stresses: pH 4.5-8.5, 7.5% NaCl salinity, and drought-mimicking low water activity (a _w 0.950, 32% sorbitol). In wheat trials, ST3M-39a inoculation significantly increased the growth parameters (p < 0.05 vs. those of the uninoculated controls), resulting in 85-92% of the biomass stimulation observed with diammonium phosphate (DAP) fertilizer. This multifunctional stress tolerance, coupled with its near-fertilizer efficacy, positioned ST3M-39a as a transformative bioinoculant for degraded soils. Field validation of its agricultural deployment and ecological impact is now pivotal.