Bioremediation of chromium (VI) from mining-contaminated soil using Klebsiella sp. (BH-A1): environmental implications.

The present investigation aimed to isolate and identify a novel bacterium from chromium (VI)-contaminated soil samples collected from the Gorbi mine area, Singrauli coalfield, evaluates its potential for Cr(VI) reduction to Cr(III) and enhances environmental and operational conditions to apply this in bioremediation of Cr-contaminated soils. A bacterium was newly isolated from contaminated soils of coal mines for chromium (VI) reduction and identified as Klebsiella sp. (BH-A1) using 16S rRNA gene sequencing. Calcium chloride and sodium alginate solutions were used to immobilize the bacterial cells of isolated Klebsiella sp. Bacteria beads (Klebsiella sp. BH-A1) were tailored to reduce 10 µg/g Cr(VI)-contaminated soil under varied environmental factors such as bead biomass (200-1000 mg), pH (5-8), temperature (25-35 °C), and nutrient sources. Beads of Klebsiella sp. (BH-A1) (1000 mg/g) were efficient for 87% reduction of 10 µg/g Cr(VI) present in the soil at pH 7, 30 °C, within a six-hour contact period. Fourier transform infrared spectroscopy analyses reveal varied functional groups like -OH, -NH, and -COOH in Cr-treated bacterial beads. Functional groups corroborate their involvement in Cr(VI) and Cr(III) absorption on the cell surface of bacteria. Chromium-treated Klebsiella sp. (BH-A1) cell size was wider due to chromium absorption than the non-treated bacterial cells after SEM analyses. The energy dispersive X-ray plot has proven the 0.41 weight percent chromium accumulation inside the bacterial cells. Moreover, XPS analyses of Cr-treated bacterial cells indicate reduced Cr(VI) into Cr(III). The finding further suggests that Klebsiella sp. (BH-A1) might be a new prospect for potential application in Cr detoxification from Cr-contaminated soil. The limitations of this research include the accumulation of hazardous metabolic products due to low diffusion rates, the formation of thick biofilms blocking bead pores, and interrupted substrate transport from the bulk liquid to immobilized cells.