Biosorption and bioaccumulation of chromate from aqueous solution by a newly isolated Bacillus mycoides strain 200AsB1

Abstract

Microbial chromate (Cr⁶⁺) reduction and consequent chromite (Cr³⁺) biosorption have exhibited potential for the remediation of chromium (Cr)-contaminated water. However, few microorganisms that can accumulate amounts of Cr⁶⁺ in their cells have been reported. In this study, a new Cr⁶⁺-resistant bacterium was isolated and characterized by physiological, biochemical and molecular tests. Its Cr⁶⁺ resistant ability, removal efficiency and mechanisms were also investigated at different initial Cr⁶⁺ concentrations, solution pHs and incubation temperatures. Results showed that the strain 200AsB1 was a typical bacterium belonging to Bacillus mycoides and tolerated 125 mg L⁻¹ Cr⁶⁺ (34 h-LC₅₀ = 63.9 mg L⁻¹). Although the strain preferred to grow at low pH without Cr⁶⁺ stress, it only grew well and removed Cr⁶⁺ from neutral or alkaline solutions. Similar to the pH experiment, the strain grew better at low temperature than at high temperature, regardless of Cr⁶⁺ amendment, but high temperature promoted Cr⁶⁺ removal. By analyzing the functional groups' change on the bacterial surface by Fourier transform infrared spectroscopy, our data indicated that N–H and O–H groups from N-methyl-glucamine were involved in Cr⁶⁺ adsorption. While Cr concentrations on the bacterial surface were 0.53–0.96 mg L⁻¹, the cell Cr concentration was up to 273 mg kg⁻¹, both of which might contribute to the efficient Cr⁶⁺ removal from aqueous solution. Our study demonstrated that B. mycoides strain 200AsB1 could provide new opportunities to remediate Cr-contaminated water through both biosorption and bioaccumulation processes.