Ferrihydrite reduction and vivianite biomineralization mediated by iron reducing bacterium Shewanella oneidensis MR-4

Abstract:

[Objective] To explore the mineralogical, chemical and microscopic properties of extracellular vivianite formation induced by iron-reducing bacteria Shewanella oneidensis MR-4. [Methods] MR-4 cells grown with 30 mmol/L of lactate and 10 mmol/L of amorphous ferrihydrite, which were used as electron donor and electron acceptor, respectively. The medium was buffered with 30 mmol/L[HCO₃^-] and 5 mmol/L[PO₄^3-], and the culture was incubated at 30℃. The headspace of serum bottle flushed with N₂/CO₂(V/V, 80/20). The pH, biomass and[Fe(Ⅱ)] of the culture were measured by sampling at different time points. Meanwhile, the combination of X-ray diffraction, scanning electron microscope, laser Raman and transmission electron microscope approaches were applied to characterize the mineralogical, chemical and morphological properties of products produced within the culture. [Results] MR-4 could couple the reduction of Fe(Ⅲ) with the oxidation of lactate for their cell growth and mineral transformation of Ferrihydrite. Specifically, ferrihydrite was initially transformed to nanometer-sized magnetite particles and majorly to micrometer-sized vivianite with bladed and fibrous morphologies finally. [Conclusion] The biomineralization process and products by MR-4 were strongly affected by environmental conditions such as the types and concentration of anions. In this case with relatively high[PO₄^3-] within the culture, ferrihydrite was initially converted to nanometer-sized magnetite, and was transformed into vivianite dominantly at the end of the culture. The result of this paper provides a new insight for comprehensive understanding of the microbial induced biomineralization of iron-reducing bacteria and its role in the iron element biogeochemical cycle.

Key words:iron-reducing bacteria;biomineralization;magnetite;vivianite;electron microscopy;laser Raman;X-ray diffraction