An effective sustainable strategy: Plant Growth Promoting Rhizobacteria (PGPR), Bacillus atrophaeus, in maize plants against challenging environments

Drought and heavy metal toxicity are significant stress factors that adversely affect plant growth and development . Bacillus atrophaeus , a plant growth-promoting bacterium, plays a crucial role in enhancing plant resistance to stress. Additionally, B. atrophaeus may enhance the ability of plants to survive and thrive in stressful conditions by enabling more efficient content of nutrients. In this context, this research investigates the impact of B. atrophaeus seed priming on growth, photosynthetic parameters, and antioxidant activities in maize under arsenic (As, 100 μM) and/or drought (PEG, 10 %) stress. Our study found that the relative growth rate (RGR) of maize seedlings under As and drought stress was reduced by 38 % and 50 %, respectively, with a 35 % decrease in relative water content (RWC) under combined As+PEG stress. However, B. atrophaeus inoculation mitigated the negative effects of stress factors on growth and maintained water relations. Both drought and As stress caused a decrease in gas exchange parameters and maximum quantum yield of PSII (F v /F m ). Bacterial inoculation reversed this situation and increased photosynthetic performance. It was determined that H 2 O 2 content of maize seedlings increased by 65.8 % under As+PEG conditions. H 2 O 2 accumulation was visualized and confirmed using confocal microscopy . B. atrophaeus priming elevated SOD , CAT , APX , and GPX activities , and also supported the maintenance of cellular redox state by inducing the ascorbate-glutathione (AsA-GSH) cycle. In addition, B. atrophaeus inoculation positively influenced plant growth by increasing the content of micro- and macro-nutrients such as Ca, K, Mg, and Fe. Furthermore, B. atrophaeus conferred tolerance to heavy metal stress by significantly reducing As uptake in the roots. Consequently, it was found that seed inoculation with B. atrophaeus increased antioxidant system activity in maize seedlings against drought, As, and their combination, reduced oxidative damage by regulating photosynthetic reactions, growth, and water relations, and enhanced stress resilience. Additionally, this study contributes to elucidating the effects of bacterial inoculation on plants subjected to drought and heavy metal pollution.