Genome-Resolved Insights Into Phosphate-Solubilizing Bacteria From Wild Rice Rhizosphere Reveal Adaptive Strategies for Phosphorus Cycling Under Acid-Saline Stress in the Mekong Delta, Vietnam.

Phosphorus (P) limitation constrains crop productivity in acid and saline soils of the Mekong Delta, where low P availability rather than total P content limits plant growth. This study aimed to isolate phosphate-solubilizing bacteria (PSB) from the rhizosphere of wild rice (Oryza rufipogon) and to investigate their functional traits and genomic basis of adaptation. A total of 43 bacterial isolates were obtained, of which 10 showed strong phosphate-solubilizing activity (PSI 1.5-2.5). Selected strains released up to ~900 mg L-1 soluble phosphorus after 10 days, with strain GC1.3 exhibiting high tolerance to pH 4-7 and 0.1%-1.0% NaCl, and exceeding 1000 mg L-1 at pH 6. Whole-genome sequencing revealed that GC1.3 belongs to Enterobacter hormaechei (ANI = 95.93%) with a complete genome of 4.78 Mb. Genomic analysis identified key genes involved in phosphate mobilization, including gcd and pqqC (organic acid production), phnC-phnD (phosphonate uptake), and ppk-ppx (polyphosphate metabolism), along with multiple stress-response systems related to ion homeostasis, osmoprotection, and oxidative stress. Notably, GC1.3 harbors 411 phosphate-related genes, exceeding those of reference strains. These findings demonstrate that wild rice rhizosphere harbors metabolically versatile PSB capable of sustaining phosphorus cycling under acid-saline stress. Strain E. hormaechei GC1.3 shows strong potential as a biofertilizer candidate for improving P availability in stress-prone agricultural soils.