Sunlight-triggered Synergy of Hematite and Shewanella oneidenesis MR-1 in Cr(VI) ReductionThis study investigated molecular mechanisms of Cr(VI) removal by hematite particles and Shewanella oneidensis MR-1 (MR-1) in dark versus under sunlight irradiation using both batch experiments and photoelectrochemical analysis.

Abstract:

Electron transfer between the natural semiconducting minerals (e.g., Hematite) and microorganisms is closely related to microbial metabolism, biogeochemical processes and utilization of solar energy in the earth surface environment. Recent studies have suggested that non-autotrophic bacteria with the ability of extracellular electron-transfer (EET) (e.g., Geobacter, Shewanella) can transfer bio-electrons to fill photo-generated holes of semiconductor minerals. As a result, photoelectrons can be sufficiently separated from photo-generated holes and participate in the biogeochemical processes in surrounding environments. However, in the previous studies, this conceptual model was mostly tested in electrochemical systems with externally applied potentials. This study investigated molecular mechanisms of Cr(VI) removal by hematite particles and Shewanella oneidensis MR-1 (MR-1) in dark versus under sunlight irradiation using both batch experiments and photoelectrochemical analysis. By studying kinetics and extents of Cr(VI) removal and lactate metabolism under different experimental conditions, quantifying the electron flow in the Cr(VI)-microbe-mineral system, measuring cell viability with time, and characterizing Cr species in end-products, we revealed that sunlight irradiation can efficiently promote Cr(VI) reduction by hematite and MR-1 and also reduce Cr toxicity to MR-1. The findings are helpful to extend our understanding about the role of mineral-microbe interactions in energy conversion, electron transfer, and contaminant transport in natural environments.