Methylobacterium sp. EIKU22 as a strategic bioinoculant for uranium and arsenic mitigation in agricultural soil: a microbial solution for sustainable agriculture.

Mitigation of potentially toxic elements (PTEs) such as uranium (U) and arsenic (As), and fulfilment of global food demand requires a sustainable approach. Therefore, a multiple PTE-tolerant Methylobacterium sp. EIKU22 was explored for its bioremediation and biofertilization potential. This multi-metal tolerant isolate removed 29.88% U (initial dose: 100 mg L^-1, pH 4.0, biosorption 3.74 mg g^-1) after 14 days, following pseudo-second-order (PSO) kinetics. The isolate also showed 54% As(III) [pseudo-first-order kinetic; 3.72 mg g^-1]; and ~ 37% As(V) (PSO; 2.4 mg g^-1) removal within 60 min with the same initial dosing of either As(III) or As(V). Moreover, the strain precipitated > 96.5% and ~ 97% of U using released phosphate from inorganic and organic sources, respectively. Further analysis with inorganic phosphate showed > 31%, > 41% and > 98% of U precipitation from initial doses of 1000, 500 and 100 mg L^-1 within 5 min. Methylobacterium sp. EIKU22 expresses the potential to solubilize ~ 178% phosphate, 169.8% potassium, 156-213% zinc within 6 days, and was able to withstand a pH range of 4.0-8.0, temperature range of 20-35 °C, and exhibited resilience to up to 10% NaCl exposure despite being affected by UV exposure. Further, the isolate showed to grow in nitrogen-free media and produce IAA, ammonia, siderophore, ACC deaminase, cellulase and catalase, suggesting potential application in plant growth promotion. The isolate harbours amoA, and nifH genes and imparts better survivability and vegetative growth in the rice seedling. These findings showcase the strain's dual applicability. However, further investigation is needed to generalize the findings.