Integrated Mineralogical, Metabolomic, and Gene Expression Analysis of the Phosphate- Solubilizing Mechanism of Pseudomonas sp. PSB-13

Background and Aims Phosphate-solubilizing microorganisms (PSMs) are pivotal for soil phosphorus (P) cycling and sustainable agriculture. This study aims to screen a high-efficiency PSM and systematically decipher its dissolution mechanisms for tricalcium phosphate (Ca-P), iron phosphate (Fe-P), and aluminum phosphate (Al-P). Methods A highly efficient phosphate-solubilizing bacterium, strain PSB-13, was isolated and identified as Pseudomonas sp. via 16S rDNA sequencing. Its solubilizing capacity for three insoluble phosphates (Ca-P, Fe-P, Al-P) was quantitatively evaluated in liquid culture. An integrated approach, including scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR), was employed to characterize mineralogical changes. Untargeted metabolomics and RT-qPCR were further utilized to profile exometabolites and quantify the expression of phosphate-solubilizing-related genes, respectively. Results Results showed PSB-13 was identified as Pseudomonas sp., with the highest solubilizing capacity for Ca-P (268.64 mg/L), followed by Fe-P (38.97 mg/L) and Al-P (20.09 mg/L). Mineralogical characterization (SEM-EDS, XRD, FTIR) provided direct evidence of surface erosion, elemental composition changes, and structural alterations on all three phosphates after bacterial treatment. Untargeted metabolomics indicated glutathione metabolism and pyrimidine metabolism were significantly enriched in all insoluble phosphate treatments; key organic acids included malonic acid/lactobionic acid (Ca-P), malonic acid/maleamic acid (Fe-P), and glutamic acid/L-histidine (Al-P). Reverse transcription quantitative polymerase chain reaction (RT-qPCR) showed upregulated expression of genes related to organic acid production. Conclusion This study provides new insights into the phosphate-solubilizing mechanisms of PSB-13 and lays a theoretical foundation for its application as a microbial fertilizer