Genomic and physiological insights into salt-tolerant PGPB Citrobacter freundii S5 isolated from halite for salinity stress mitigation in wheat (Triticum aestivum L.)

Globally, salinisation is one of the major causes of soil degradation, threatening agricultural and food security. Salinity stress affects plants' ionic and osmotic balance, negatively affecting physiology, morphology, and biochemical metabolism. Salinity stress generates reactive oxygen species (ROS) that damage DNA, resulting in plant cell death and ultimately reducing crop productivity. Salt-tolerant plant growth-promoting bacteria (ST-PGPB) are widely known for mitigating salinity stress. In the current study, halite from a salt mine site in Himachal Pradesh was targeted for the isolation of ST-PGPB. Twelve bacterial strains were isolated, and one potential PGPB, Citrobacter freundii S5, was selected for this study . PGPB-S5 was bio-prospected using physiological growth profiling, PGP attributes, and whole-genome sequencing. Furthermore, its effect on wheat ( Triticum aestivum L . ) was evaluated under salinity stress. PGPB-S5 significantly increased total plant biomass and relative water content (18%) and reduced electrolyte leakage (27.4%); however, no difference was observed in antioxidant enzyme activity. Whole-genome analysis revealed that the PGPB-S5 harbours several functional genes that regulate direct and indirect mechanisms of plant growth promotion through phytohormone production, nutrient acquisition, and stress alleviation. Conclusively, the findings suggest that the selected bacteria are potential candidates to enhance stress tolerance and increase crop yield in such saline agroecosystems.