Investigation of the interface reaction mechanism in Shewanella oneidensis MR-1 during chromium (VI) reduction enhanced by pyrite

Abstract

Mineral-microbe interaction is crucial in driving chromium biogeochemical cycling in the environment. In this study, a system involving Shewanella oneidensis MR-1 and pyrite was constructed to explore their molecular interaction process, and the mechanism behind their cooperative removal of Cr(VI) was clarified. Batch experiment results indicate a synergistic Cr(VI) removal effect between MR-1 and pyrite, as the Cr(VI) removal rate in the MR-1 + pyrite + Cr(VI) system (97.3 %) was higher than the combined rate of the MR-1 + Cr(VI) system (25.8 %) and the pyrite + Cr(VI) system (9.36 %). Additionally, pyrite was proven to stimulate MR-1 by restoring its reducing power under Cr(VI) stress, providing shelter and promoting colonization for MR-1. This is evidenced by the fluctuating c-Cyt levels in the MR-1 + pyrite + Cr(VI) system, which initially decreased and then increased, a pattern not observed in the MR-1 + Cr(VI) system. Furthermore, the pyrite surface was identified as the primary reaction site for Cr(VI) reduction, forming a bacterial-mineral interface conducive to reciprocal interaction. Specifically, Fe(III) and S⁰, the reaction products of pyrite and Cr(VI), accumulated on the pyrite surface and served as electron acceptors for MR-1, supporting Fe and S reduction processes. Moreover, these Fe and S reduction processes are synergistic and mutually reinforcing. Their reduction products, S^2- and Fe²⁺, with strong reducing properties, further facilitated the transformation of Cr(VI) to Cr(III). This research achievement will enhance our understanding of the bacteria-pyrite interaction mechanisms and their role in driving chromium migration and transformation.

Keywords: Cr(VI) reduction; Iron/sulfur cycle; Pyrite; Reciprocal interaction; Shewanella oneidensis MR-1.