Isolation and characterization of rhizobacteria from lentil for arsenic resistance and plant growth promotion

Low-cost microbial remediation strategies serve as a viable and potent weapon for curbing the arsenic menace. In the present study, two arsenic-resistant bacteria were isolated from the contaminated lentil rhizosphere in Gangetic plain of eastern India. LAR-21 (Burkholderia cepacia, MW356875) and LAR-25 (Burkholderia cenocepacia, MW356894) could remove 87.6% and 85.9% of arsenite (10 mM) from the liquid culture medium in laboratory condition. They were highly resistant to arsenate and arsenite and also had a high arsenite oxidase activity. LAR-21 showed the highest level of minimum inhibitory concentration value of 390 mM for arsenate and 31 mM for arsenite. The same strain was found to show highest arsenite oxidase activity, i.e., 5.2 nM min⁻¹ mg⁻¹of protein. These two strains further possess potential plant growth-promoting characteristics like indole acetic acid production (5–15 mM IAA mL⁻¹), 1-aminocyclopropane-1-carboxylate deaminase (8–21 nM α-keto butyrate mg protein⁻¹ h⁻¹), nitrogenase activity (3–8.99 nM ethylene mg cell protein⁻¹ h⁻¹), siderophore production (17–22.1 µM deferoxamine mesylate mL⁻¹), phosphate solubilization (261–453 µg mL⁻¹) under arsenic stress condition. The plant growth promotion of the strains was further validated by pot study of lentil by assessing their agronomic and growth-related traits, and potential to recover from arsenic stress (17.2–21.2% arsenic reduction in root and shoot, 16–19.2% in leaf and pod, and 15–23% reduction in seeds). The LAR-21 strain, thus, emerged as the most suited candidate for bioremediation and plant (lentil) growth promotion in arsenic polluted environment.