Simultaneous organic/inorganic phosphate solubilization by Staphylococcus succinus NG-9 under saline-alkali conditions: Insights into its characteristics, mechanisms, and potential applications

The high salinity and alkalinity of saline-alkali soil limit the growth of plants and agricultural productivity worldwide, and plant growth-promoting rhizobacteria can effectively improve the tolerance of crops to saline-alkali stress. The highly efficient bacterial strain NG-9 that can solubilize phosphate was isolated from a rhizosphere soil sample in saline-alkali land and identified as Staphylococcus succinus based on analyses of its phenotype and 16S rRNA sequence. It showed a remarkable ability to solubilize both inorganic phosphate (up to 450.36 mg/L) and organic phosphate (up to 333.15 mg/L) under saline-alkali conditions. In addition, this strain had numerous plant growth-promoting traits at 5.0% NaCl and pH 9.0, including but not limited to the production of 1-aminocyclopropane-1-carboxylate deaminase (7.37 µmol α-ketobutyric acid/mg protein/h), siderophores (36.63%), indole-3-acetic acid (4.14 µg/mL), and extracellular polymeric substances (1.04 g/L). Furthermore, genomic and metabolic analyses confirmed the presence of multiple functional genes and key metabolites related to the promotion of plant growth and ability to adapt to saline-alkali conditions. Notably, the germination rate, length and numbers of roots, and shoot length of wheat ( Triticum aestivum ) seeds increased by 1.04%–162.5%, 13.18%–116.32%, 20.22%–42.86%, and 20.78%–124.42%, respectively, when Staphylococcus succinus NG-9 was inoculated under saline-alkali conditions. These findings strongly suggest that S. succinus NG-9 can be developed as a multifaceted biofertilizer to reclaim and utilize saline-alkali land. IMPORTANCE Plant growth-promoting rhizobacteria can effectively improve the tolerance of crops to saline-alkali stress. A highly efficient phosphate-solubilizing bacterial strain was isolated from a rhizosphere soil sample in saline-alkali land and identified as Staphylococcus succinus NG-9. This strain showed a remarkable ability to solubilize both inorganic phosphate and organic phosphate under saline-alkali conditions. In addition, this strain was subjected to an in-depth study of the mechanisms and potential applications using genomic sequencing and annotation, untargeted metabolomics, and a seed germination test. These results strongly suggest that S. succinus NG-9 can be developed as a multifaceted biofertilizer to reclaim saline-alkali lands.