Dissimilatory Iron [Fe(III)] Reduction by a Novel Fermentative,Piezophilic Bacterium Anoxybacter fermentans DY22613T Isolated from East Pacific Rise Hydrothermal Sulfides

Dissimilatory iron-reducing microorganisms play an important role in the biogeochemical cycle of iron and influence iron mineral formation and transformation. However, studies on microbial iron-reducing processes in deep-sea hydrothermal fields are limited. A novel piezophilic, thermophilic, anaerobic, fermentative iron-reducing bacteria of class Clostridia, named Anoxybacter fermentans DY22613^T, was isolated from East Pacific Rise hydrothermal sulfides. In this report, we examined its cell growth, fermentative metabolites, and biomineralization coupled with dissimilatory iron reduction. Both soluble ferric citrate (FC) and solid amorphous Fe(III) oxyhydroxide (FO) could promote cell growth of this strain, accompanied by increased peptone consumption. More acetate, butyrate, and CO₂ were produced than without adding FO or FC in the media. The highest yield of H₂ was observed in the Fe(III)-absent control. Coupled to fermentation, magnetite particles, and iron-sulfur complexes were respectively formed by the strain during FO and FC reduction. Under experimental conditions mimicking the pressure prevailing at the deep-sea habitat of DY22613^T (20?MPa), Fe(III)-reduction rates were enhanced resulting in relatively larger magnetite nanoparticles with more crystal faces. These results implied that the potential role of A. fermentans DY22613^T in situ in deep-sea hydrothermal sediments is coupling iron reduction and mineral transformation to fermentation of biomolecules. This bacterium likely contributes to the complex biogeochemical iron cycling in deep-sea hydrothermal fields.