Biochemical Characterization and Potential of Bacillus safensis Strain SCAL1 to Mitigate Heat Stress in Solanum lycopersicum L.

Endophytic microbes promote plant growth through various biochemical mechanisms and assist plants in resuming their morpho-physiological traits under abiotic stresses. The current study was conducted to investigate the plant growth promotion properties and biochemical characterization of Bacillus safensis (SCAL1) under various heat stress regimes. Further investigations aimed to understand the potential of heat-tolerant B. safensis (SCAL1) in amelioration of heat stress in two varieties of tomato ( Solanum lycopersicum cv. Riogrande and Sweetie). Properties characterized include 1-aminocyclopropane-1-carboxylate deaminase (ACC deaminase) (0.84–0.96 μM/mg protein/h) and exopolysaccharide (EPS) (0.73–0.92 mg ml −1 ) under normal and heat stressed conditions. An increased level of ACC deaminase (12.5%) and EPS (20.65%) was observed under heat stress as compared to normal conditions. B. safensis also produced plant growth regulators such as indole acetic acid (IAA) (0.71, 0.57, and 0.49 μg ml −1 ), gibberellic acid (GA 3 ) (19.4, 18.2, and 19.2 μg ml −1 ), and kinetin (32.07, 27.3, and 26.8 μg ml −1 ) under heat stress and control conditions. IAA and kinetin production were slightly reduced under heat stress conditions compared to control conditions. A greenhouse experiment was carried out to analyze the bacterial potential to promote plant growth under heat stress conditions. Inoculation of both tomato varieties with B. safensis significantly improved plant growth parameters, antioxidant enzyme activities, and chlorophyll content under heat stress. The results suggest that inoculating tomato with thermo-tolerant plant growth-promoting endophytic bacterium may provide an eco-friendly management strategy to mitigate heat stress.