Ameliorating drought resistance in Arabidopsis and alfalfa under water deficit conditions through inoculation with Bacillus tequilensis G128 and B. velezensis G138 derived from an arid environment

• Bacillus tequilensis G128 and B. velezensis G138, isolated from an arid environment, exhibit distinctive growth-promoting and drought-tolerance capabilities, positioning them as promising candidates for further investigation. • Both strains can alleviate drought stress in Arabidopsis and alfalfa seedlings by improving phenotypic traits and physiological responses. • These strains mitigate drought-induced damage in alfalfa seedlings by enhancing antioxidant enzyme activities, elevating the levels of osmoregulatory compounds, curbing the accumulation of peroxides, and upregulating the expression of drought-responsive genes. Drought stress is a critical factor limiting plant growth and agricultural productivity, causing significant physiological and biochemical disruptions. This study addresses the gap in research on enhancing plant drought tolerance through plant growth-promoting bacteria (PGPB), focusing on two Bacillus strains, B. velezensis and B. tequilensis , isolated from the arid soils of Qinghai province, China. Both isolates have shown growth-promoting potential but their role in improving drought tolerance, especially in forage crops like alfalfa, has been understudied. The research firstly identified both isolates with phylogenetic trees based on 16S rRNA genes and evaluated their growth-promoting abilities. Then pot experiments were conducted to assess the physiological, biochemical, and gene expression responses of Arabidopsis or alfalfa inoculated with these isolates under drought conditions. Results revealed significant improvements in shoot and root growth, biomass, and chlorophyll content in inoculated plants under drought stress. Additionally, the isolates enhanced antioxidant enzyme activities (SOD, POD, and CAT) and reduced oxidative stress markers (H₂O₂, O₂⁻, and MDA), while promoting the accumulation of osmolytes like proline and soluble sugars. Moreover, inoculated plants showed upregulated expression of key drought-responsive genes, such as MsWRKY8 and MsNCED1 , indicating enhanced drought tolerance at the molecular level. This research underscores the potential of these Bacillus isolates as a basis for developing eco-friendly biofertilizers to boost agricultural productivity in drought-prone regions.