Phosphate-Solubilizing Bacteria: From Phosphate Mobilization to Improved Plant Nutrition

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Abstract
Phosphorus (P) is a vital macronutrient required for plant growth and development; however, only a small fraction is readily available for plant uptake because much of the soil phosphorus becomes immobilized through chemical fixation. Moreover, dependence on finite phosphate rock reserves and the intensive use of mineral phosphorus fertilizers increase production costs and raise environmental concerns, emphasizing the need for more sustainable phosphorus management strategies. Phosphate-solubilizing bacteria (PSB) are key drivers of microbial phosphorus cycling, enhancing phosphorus bioavailability by transforming insoluble inorganic and organic phosphorus compounds into forms that plants can readily absorb. This process is mediated by the secretion of organic acids, phosphatases, phytases, and other metabolites involved in phosphorus mobilization. In addition to increasing phosphorus bioavailability, PSB can enhance overall nutrient-use efficiency, promote root growth and architecture, support biological nitrogen fixation, and strengthen plant resilience to abiotic stresses, including drought, salinity, and temperature extremes. Owing to these multiple plant growth-promoting functions, PSB are increasingly recognized as promising bioinoculants that can improve crop productivity, enhance climate resilience, and reduce reliance on synthetic phosphorus fertilizers. This narrative review provides a comprehensive overview of recent advances in understanding PSB-mediated microbial phosphorus cycling, with particular emphasis on the mechanisms underlying phosphorus solubilization, interactions with plant roots, and contributions to sustainable crop production. Evidence from laboratory, greenhouse, and field studies is synthesized to evaluate PSB-mediated mechanisms, plant responses, and their potential for agricultural application. The review also highlights key barriers to the widespread adoption of PSB, including inconsistent field performance and challenges associated with commercialization. Addressing these limitations could support the development of cost-effective biofertilizers that increase phosphorus-use efficiency, reduce dependence on mineral fertilizers, lower production costs, and enhance farm profitability while contributing to sustainable agriculture.

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