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<p>Hexavalent chromium [Cr(VI)] removal was evaluated using two facultative anaerobic bacteria isolated from a microbial mat near a chromite mining site: <i>Bacillus</i> sp. S9 (Gram-positive) and <i>Enterobacter</i> sp. Z11 (Gram-negative). Both strains effectively removed Cr(VI) under anaerobic conditions, with total removal efficiencies of 98.3 ± 0.6% and 97.2 ± 0.9%, respectively. The bacteria reduced Cr(VI) to trivalent chromium [Cr(III)], with this reduction occurring extracellularly in the supernatant, on cell surfaces, and intracellularly. Chromate reductase assays and spectroscopic analyses confirmed the predominant biological reduction of Cr(VI) to Cr(III), with minor formation of elemental chromium [Cr(0)]. Surface analyses showed Cr deposition on the surface of <i>Bacillus</i> sp. S9 (13.3 ± 0.5%) and <i>Enterobacter</i> sp. Z11 (33.9 ± 2%), with functional groups such as OH-NH, methyl-C-H, C = O/COO, C-N, N-H, PO<sub>4</sub><sup>3-</sup>, metal–O, and Cr(VI)–O bonds contributing to biosorption. Both strains secreted approximately two-fold more extracellular polymeric substances (EPS) after exposure to Cr(VI), thereby enhancing metal binding. Intracellular Cr accumulation was also observed, with a total amount of 3.9 ± 0.3&#xa0;mg L⁻¹ in <i>Bacillus</i> sp. S9 and 6.4 ± 0.3&#xa0;mg L⁻¹ in <i>Enterobacter</i> sp. Z11. These results demonstrate that facultative anaerobes from microbial mats effectively reduce, adsorb, and accumulate Cr species, underscoring their potential application in bioremediation of Cr-contaminated environments under varying oxygen conditions.</p>

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Removal of hexavalent chromium by facultative anaerobic strains Bacillus sp. S9 and Enterobacter sp. Z11 from a mining site microbial mat

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  • 发表日期：

    2026年5月15日

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  • Mohammad Tariq Ali Khan,
  • Wael Ismail,
  • El-Said I. El-Shafey,
  • Raeid M. M. Abed

摘要

Hexavalent chromium [Cr(VI)] removal was evaluated using two facultative anaerobic bacteria isolated from a microbial mat near a chromite mining site: Bacillus sp. S9 (Gram-positive) and Enterobacter sp. Z11 (Gram-negative). Both strains effectively removed Cr(VI) under anaerobic conditions, with total removal efficiencies of 98.3 ± 0.6% and 97.2 ± 0.9%, respectively. The bacteria reduced Cr(VI) to trivalent chromium [Cr(III)], with this reduction occurring extracellularly in the supernatant, on cell surfaces, and intracellularly. Chromate reductase assays and spectroscopic analyses confirmed the predominant biological reduction of Cr(VI) to Cr(III), with minor formation of elemental chromium [Cr(0)]. Surface analyses showed Cr deposition on the surface of Bacillus sp. S9 (13.3 ± 0.5%) and Enterobacter sp. Z11 (33.9 ± 2%), with functional groups such as OH-NH, methyl-C-H, C = O/COO, C-N, N-H, PO43-, metal–O, and Cr(VI)–O bonds contributing to biosorption. Both strains secreted approximately two-fold more extracellular polymeric substances (EPS) after exposure to Cr(VI), thereby enhancing metal binding. Intracellular Cr accumulation was also observed, with a total amount of 3.9 ± 0.3 mg L⁻¹ in Bacillus sp. S9 and 6.4 ± 0.3 mg L⁻¹ in Enterobacter sp. Z11. These results demonstrate that facultative anaerobes from microbial mats effectively reduce, adsorb, and accumulate Cr species, underscoring their potential application in bioremediation of Cr-contaminated environments under varying oxygen conditions.