Chromium is often found in groundwater and wastewater as a natural contaminant or from man-made sources. Hexavalent chromium (Cr(VI)) is a highly toxic and carcinogenic substance, while trivalent chromium (Cr(III)) is considerably less toxic. Bioremediation using bacteria to reduce Cr(VI) to Cr(III) provides an environmentally friendly approach for the removal of Cr from water. In most natural and engineered environments, bacterial cells often attach onto surfaces and develop into sessile communities known as biofilms. Comparing to their planktonic counterparts, biofilms have been reported to be more tolerant to harsh environmental conditions and, thus, have been increasingly applied to the efficient removal of toxic contaminants from water and wastewater. Biofilms of Shewanella oneidensis, a bacterium capable of reducing various metals, could remove toxic metals from the aqueous phase. However, the exposure to Cr(VI) causes dispersal of S. oneidensis biofilms, resulting in a decreased performance of the biofilm-based bioprocesses. In this study, we demonstrated that the performance of S. oneidensis biofilms in removing Cr(VI) could be significantly enhanced through increasing biofilm cohesiveness. One hyper-adherent mutant strain CP2-1-S1 exhibiting an enhanced capability in biofilm formation was obtained through a random transposon mutagenesis library screening. Quantitative analysis showed that, compared with the wild-type (WT), the mutant strain CP2-1-S1 formed stronger biofilms with a significantly lower cell detachment rate in the presence of Cr(VI) and removed Cr(VI) more efficiently from the aqueous phase. The X-ray absorption near edge structure (XANES) analyses revealed that Cr in biofilms of both WT and CP2-1-S1 was Cr(III), suggesting that the mechanism of Cr(VI) removal by the biofilms is Cr immobilization through reducing Cr(VI) to Cr(III). Taken together, our results demonstrate a novel biofilm-based strategy in removing toxic metal(loid)s from water by engineering metal-reducing biofilms to achieve an efficient and robust performance.

Efficient and robust removal of chromium using engineered metal-reducing biofilms

249th National Meeting (2015)

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