Phytoremediation of hexavalent chromium from soil via Pennisetum pedicellatum and chromium-resistant rhizospheric microflora: a synergistic approach.

Hexavalent chromium [Cr(VI)] is a persistent, highly toxic, and bioaccumulative contaminant that poses serious risks to soil ecosystems and human health. This study investigated the phytoremediation potential of Pennisetum pedicellatum and characterized chromium-associated rhizospheric bacteria in Cr(VI)-contaminated soil. A 60-day greenhouse pot experiment was conducted using four Cr(VI) treatments: control (T0), 25 mg kg⁻1 (T1), 50 mg kg⁻1 (T2), and 100 mg kg⁻1 (T3). Plant and soil samples were collected at 15-day intervals to evaluate growth, biomass, biochemical responses, and chromium accumulation. Chromium uptake increased with both treatment concentration and exposure time, with the highest accumulation observed in T3, reaching 58.55 mg kg⁻1 in roots and 20.23 mg kg⁻1 in shoots. Chromium was preferentially retained in the root system, while prolonged exposure adversely affected root and shoot growth despite relatively higher biomass production under T3. The calculated bioaccumulation factor (BAF) and translocation factor (TF) confirmed P. pedicellatum's ability to accumulate chromium, with root sequestration indicating phytostabilisation as the predominant remediation mechanism. In addition, five chromium-associated rhizospheric bacterial isolates were identified through biochemical characterization and 16S rRNA gene sequencing as Bacillus foraminis, Bacillus wudalianchiensis, Bacillus australimaris, Bacillus licheniformis, and Bacillus paramycoides. Although these isolates were successfully identified, their functional roles in chromium resistance, Cr(VI) reduction, biosorption, and plant growth promotion were not evaluated in this study. Overall, the findings demonstrate that P. pedicellatum is a promising candidate for the phytostabilization of chromium-contaminated soils and provide a foundation for future investigations into plant-microbe-assisted phytoremediation under field conditions.