Extremohalophilic Stutzerimonas stutzeri mediated sodium complexation increases salt tolerance in wheat

Hypersaline-tolerant bacterial metabolites are believed to play a critical role in sodium detoxification and salt stress tolerance in plants; however, this mechanism needs further investigation. This study aimed to evaluate halophilic bacterial strains from hypersaline environments for their ability to increase salt tolerance in wheat seedlings through sodium‒organic acid complexation, nutrient dissolution, and improved ionic homeostasis.

The halophilic bacterial strains were isolated from hypersaline conditions of salt mines and were characterized for multiple plant growth-promoting traits. These strains were tested on wheat seedling biomass, chlorophyll, osmolyte accumulation, antioxidant defense, and ion homeostasis under salt stress. The strains were assessed for their ability to produce organic acids and increase nutrient availability by solubilizing insoluble minerals under salt stress.

The isolated bacterial strains were salt-tolerant up to 2 M NaCl stress, solubilized insoluble minerals, and produced indole acetic acid, siderophores, ammonia, hydrogen cyanide, exopolysaccharides, and various enzymes. They were identified as Stutzerimonas stutzeri (strains MRK6 and MRK20) and Pseudomonas aeruginosa (strains MRK7 and MRK11). S. stutzeri MRK6 showed the highest increase in wheat seedling growth, chlorophyll, osmolytes accumulation, antioxidant enzymes, and ion homeostasis by increasing potassium uptake and modulating sodium toxicity under 100 mM salt stress. This increased nutrient availability from insoluble minerals.

The halophilic S. stutzeri MRK6 increased salt tolerance in wheat by increasing soil mineral dissolution, sodium detoxification, and ionic compartmentalization rather than excessive sodium uptake. This mechanism offers a promising approach for mitigating salt stress in salt-affected soils.