Bacillus paranthracis alleviates saline stress in tomato by reprogramming physiology, photosynthesis, and antioxidant activity

Salt stress is a significant environmental constraint that hinders plant growth and poses a threat to global agriculture. This study investigates the potential of the halophilic bacterium Bacillus paranthracis (strain Endo10) to enhance salt stress tolerance in tomato plants. We assessed its effects as a plant growth-promoting rhizobacterium (PGPR) by measuring growth performance, photosynthetic efficiency, spectral reflectance, and antioxidant defense mechanisms under saline conditions. The result showed that the inoculation of tomato plants with B. paranthracis significantly mitigated NaCl stress, enhancing growth and physiological performance. Treated plants exhibited significantly greater overall growth, including increased biomass and root development, compared to the NaCl controls. Chlorophyll-a fluorescence and spectral reflectance analysis confirmed superior photosynthetic efficiency (PSII) in inoculated plants. They also demonstrated stronger antioxidant activity, with elevated SOD, POD, APX, and CAT enzyme levels and reduced electrolyte leakage. These findings demonstrate that B. paranthracis improves tomato plant health under saline stress by enhancing photosynthetic efficiency, stimulating antioxidant enzyme activity, and leveraging key growth-promoting traits. Consequently, B. paranthracis is a promising bioinoculant for sustainable agriculture in salt-affected soils.