Phytoremediation of Chromium (VI)-Contaminated Soil by Euphorbia tithymaloides L. and Metagenomic Analysis of Rhizospheric Bacterial Community

This study investigated the growth of Euphorbia tithymaloides L. in soil contaminated with Cr (VI), focusing on plant development, Cr (VI) accumulation in the plant, and associated rhizosphere bacterial communities. Plants were cultivated in pots for a period of 123 days with varying Cr (VI) levels (0, 10, 20, 30, and 40 mg-kg⁻¹) in the soil. As Cr (VI) concentration increased, plant growth indicators such as fresh weight, dry weight, root length, and shoot length were observed to be decreasing. The Cr (VI) concentration peaked in plant tissues under the 40 mg-kg⁻¹ treatment, with concentrations of 397.5 mg-kg⁻¹, 98.12 mg-kg⁻¹, and 62.32 mg-kg⁻¹ in roots, stems, and leaves respectively. Whereas, the total Cr (VI) accumulation was maximum in the 30 mg-kg⁻¹ treatment due to higher plant biomass. Further, the phytoremediation efficiency of the plant was evaluated through the bio-concentration factor (BCF) and translocation factor (TF). The BCF indicated soil-to-plant heavy metal uptake capacity exceeding 1, while the TF showed root-to-shoot translocation below 1 for all treatments, implying effective phytostabilisation potential. Metagenomic analysis of rhizospheric soil highlighted dominant bacterial phyla of Firmicutes, Proteobacteria, Bacteroidetes, Actinobacteria, and Acidobacteria. Many observed bacterial taxa are metal-tolerant and commonly found in heavy metal-contaminated soil, suggesting a potential contribution to mitigating metal toxicity and enhancing plant growth. However, a comprehensive investigation into microbial communities' roles during phytoremediation requires further in-depth research.