Biological mitigation of salt stress: Role of halophilic bacteria in exopolysaccharides (EPS) and indole‑3‑acetic acid (IAA) biosynthesis.

Soil salinity postures a significant threat to agricultural productivity, exacerbating universal food security challenges. This study investigated the ability of the halophilic bacterium Halobacillus trueperi RSK CAS9 to alleviate salt stress over the exopolysaccharides (EPS) and indole-3-acetic acid (IAA) production. Growth assays revealed that bacterial proliferation decreased with increasing NaCl concentration, demonstrating moderate tolerance at lower concentrations (100-200 mM NaCl). Optimization using response surface methodology (RSM) identified pH 8.0, 15% sucrose, and a 96 h incubation period as optimal conditions for maximal EPS production (272.2 mg/L). Under various NaCl concentrations, the EPS yield peaked at 202.2 mg/L at 200 mM NaCl, suggesting enhanced stress tolerance at moderate salinity levels. SEM analysis showed morphological changes, indicating adaptive biofilm formation. Analysis of FT-IR confirmed the occurrence of hydroxyl, carboxyl, and glycosidic bonds, crucial for EPS's protective role. Additionally, IAA production peaked at 1.42 µg/mL under low saline conditions (100 mM NaCl) and decreased at higher salinities, underscoring the bacterium's potential in plant hormone responses under salted stress. Collectively, these results sustenance the potential application of halophilic bacteria as sustainable agents for managing saline stress in agricultural systems.