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, S²⁻ 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.