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

[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 [HCO_3~–] and 5 mmol/L [PO_4~(3–)],and the culture was incubated at 30 oC.The headspace of serum bottle flushed with N_2/CO_2 (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 [PO_4~(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