Salt Stress Amelioration in Brassica juncea by Halotolerant Plant Growth Promoting <i>Enterobacter xiangfangensis</i>

Background: Salinity is a significant environmental threat that affects plant development and physiological functions, thus decreasing production from agriculture. The application of halotolerant plant growth-promoting rhizobacteria (HTPGPR) is one potential solution for these issues. Methods: 21 of the 250 bacterial isolates that were evaluated for halotolerance in the present study were identified as halotolerant strains. Four of these isolates, B1, B14, B17, and B25, showed significant plant growth-promoting (PGP) properties. Results: Salinity severely impairs plant growth by disrupting cellular metabolism and inducing oxidative stress. This study evaluated the capacity of four Enterobacter xiangfangensis (E. xiangfangensis) strains (B1, B14, B17, and B25) to enhance plant growth and biochemical responses under saline conditions. GA3 quantification revealed significant variation among isolates, with strain B17 producing the highest level (49 µg/mL), followed by B14 (48 µg/mL), B25 (25 µg/mL), and B1 (16 µg/mL). In the pot experiment, plants in the negative control under salt stress exhibited elevated proline (22.10 mg/mL), total antioxidant activity (33.17 mg/mL), and total phenol content (1.09 mg/mL), indicating substantial stress damage. In contrast, bacterial inoculation significantly improved stress mitigation and growth parameters. Strain B1 recorded the highest phenol (1.69 µg/mL) and protein content (0.16 µg/mL), while strains B14 and B17 showed improved antioxidant activity (32.28 and 32.73 mg/mL, respectively) and protein content (0.14 µg/g each). All inoculated treatments enhanced fresh and dry plant biomass compared to the negative control, with B17 and B25 showing the greatest increases. The superior performance of B17 corresponds with its high GA3 production, suggesting that GA3 biosynthesis is a key mechanism contributing to stress alleviation. Overall, the results demonstrate that E. xiangfangensis strains, particularly B14 and B17, effectively enhance plant tolerance to salinity by modulating biochemical responses and promoting growth. Conclusion: The identification of these efficient strains may lead to the development of patent biofertilizers, further supporting their application in modern agricultural practices.