Isolation and characterization of acetoin-producing Bacillus species from Salicornia europaea rhizosphere with evaluation of their saline-alkaline adaptation.

Soil salinization is a major constraint on global agricultural productivity, and the application of plant growth‑promoting rhizobacteria offers an important solution for the management and utilization of saline-alkali land. In this study, we aimed to isolate and characterize beneficial rhizobacteria from the halophyte Salicornia europaea growing in coastal saline‑alkali soils, and to evaluate their potential in promoting plant growth under stressful conditions. Among 57 purified bacterial isolates, 3 acetoin‑producing strains, identified as Bacillus sp. HPZ‑9, HPZ‑47, and HPZ‑50, were selected. They produced acetoin at concentrations of 2.30 g·L-1, 2.73 g·L-1, and 2.77 g·L-1, respectively. All strains exhibited broad environmental adaptability, sustaining growth and acetoin production across a pH range of 5-11, NaCl concentrations of 0.3-1.2 mol·L-1, and under moderate drought stress simulated with 20% polyethylene glycol 6000. Notably, HPZ‑9 tolerated NaCl levels up to 2.4 mol·L-1. In pot experiments with maize seedlings, inoculation with these strains significantly increased plant height, stem diameter, leaf length, and fresh and dry biomass of shoots and roots compared to the uninoculated controls (p < 0.05). The most notable improvement was observed in dry biomass, which increased by 49% to 60%. In conclusion, the selected Bacillus strains show strong plant growth‑promoting traits and high tolerance to saline‑alkaline stress. These findings highlight their potential as effective microbial inoculants for promoting crop health and improving saline-alkali soils.