Biofilm-NOM-ferrihydrite synergy facilitate the dissimilatory iron bioreduction

Dissimilatory microbial iron reduction, a key biogeochemical process, influences the cycling of iron, hazardous metals such as arsenic, cadmium and chromium, and natural organic matter (NOM) across diverse environments like soils and aquatic systems. Despite its ecological significance, the interaction between ferrihydrite, NOM, and biofilms, particularly the synergy within these conditions, remains unclear. This study explored the bioreduction of ferrihydrite by Shewanella oneidensis MR-1 biofilms, analyzing how varying concentrations of NOM and electron donor affects this process. We developed a kinetic model to quantify iron transformation, revealing that NOM performs dual functions: as a carbon source and an electron shuttle. In carbon-rich environments, NOM acts as an electron shuttle, while insufficient carbon sources, biofilms metabolize NOM for electron transfer to ferrihydrite. The biofilm's extensive surface area facilitates the coprecipitation of NOM and ferrihydrite, enhancing electron transfer efficiency. The study noted a significant conversion of ferrihydrite into goethite and lepidocrocite, particularly at high C/Fe ratios. Additionally, integrating a coupled reactive-diffusion model, we aimed to predict iron transformation and distribution in biofilm systems. This approach emphasizes the importance of the biofilm-NOM-ferrihydrite synergy in iron biogeochemical cycles and the need for incorporating biofilm dynamics in realistic biogeochemical process models. The findings provide a new insight into the biofilm function in mediating the ferrihydrite bioreduction process in different carbon resources in real scenarios.