Phosphate-mobilizing bacterial community structure and mobilization mechanisms in tobacco rhizosphere

Phosphorus (P), one of the three primary macronutrients essential for plant growth, predominantly exists in soil as unavailable forms for plant uptake. Rhizosphere bacteria can mobilize the unavailable P through two key processes: organic phosphorus mineralization and inorganic phosphorus solubilization. Despite their ecological significance, the diversity and community structure of P-mobilizing bacteria in plant rhizospheres remain insufficiently characterized. In this study, we employed culturomics to isolate bacteria from tobacco rhizosphere and systematically evaluated their P mobilization activities. The P mobilization mechanism was analyzed through whole genome sequence analyses, and the promotion effect was evaluated by greenhouse experiment. A total of 266 P mobilization bacteria were screened, representing 41.50 % of the total isolates. These bacteria were further classified as 49 genera in four phyla: <i>Pseudomonadota</i> (63.16 %), <i>Bacillota</i> (18.80 %), <i>Bacteroidota</i> (10.15 %), and <i>Actinomycetota</i> (7.89 %), with <i>Pseudomonas</i> (25.10 %) and <i>Bacillus</i> (16.47 %) as dominant genera (>10 %). The collection comprised 232 P-mineralization bacteria (PMB) (47 genera), 126 P-solubilizing bacteria (PSB) (33 genera), and 92 dual-functional (26 genera) strains. PMB strains exhibited higher α-diversity and greater numerical abundance across all sampling sites than PSB. Genomic analyses revealed that <i>Pseudomonadota</i> strains displayed exceptional genetic flexibility, harboring more P mobilization genes than other phyla strains. Greenhouse experiments demonstrated that PSB strains significantly enhanced tobacco seedling growth, including shoot and root biomass, stem diameter and leaf area, increased both plant P content and rhizosphere soil available P concentrations. Our study provides new insights into microbial-mediated mechanisms governing phosphorus mobilization and biogeochemical cycling within plant rhizosphere ecosystems.