Biosynthesis of biogenic ferrous sulfide as a potential electron shuttle for enhanced Cr(VI) removal by Shewanella oneidensis MR-1

Abstract

Biological reduction of Cr(VI) is considered to be one of the most efficient approaches for bioremediation of Cr(VI) contaminated sites, but the slow electron transfer rate between microorganisms and Cr(VI) is a bottleneck for its practical application. The addition of ecofriendly electron shuttle can provide an effective solution to this bottleneck. In this study, a novel electron shuttle of biogenic ferrous sulfide (Bio-FeS) was biosynthesized by Shewanella oneidensis MR-1(MR-1) and employed to improve the extracellular electron transfer (EET) rate from MR-1 strain to Cr(VI) and accelerate reduction of Cr(VI). Results showed that the Cr(VI) removal rates by MR-1 was remarkably increased by 12.4 times with the addition of Bio-FeS as electron shuttle. The Cr(VI) reduction was highly pH dependent. Electrochemical analysis confirmed that the presence of Bio-FeS can accelerate EET process. The mechanism analysis indicated that Bio-FeS enhance Cr(VI) reduction by MR-1 through promoting the secretion of more extracellular polymeric substances (EPS) and enhancing EET rate. Most of Cr(VI) was converted to Cr(III) by MR-1, and then is removed from the solution in the form of precipitations, and EPS play a crucial role in Cr(VI) reduction, adsorption and complexation. This study demonstrates the significant influence of Bio-FeS on Cr(VI) reduction and provides a promising technology for the development of cost-effective Cr(VI) remediation technologies.