Formation and Stabilization of Mixed Valence Ferrihydrite on Bacterial Surfaces From Hydrothermal Vents

The dynamics of iron oxidation and reduction at hydrothermal sites is an important biogeochemical process which involves major biomineralization of iron oxides. In this study, we have studied biomineralization by the Rimicaris exoculata shrimp collected at a Mid Atlantic Ridge hydrothermal vent. The structure, morphology and impurities distributions of the minerals were analyzed by Transmission electron microscopy and electron energy loss spectroscopy. The main minerals observed are clusters of two-lines ferrihydrite, found attached to the bacterial cells present in the organ scaphognatite of the shrimp. EELS measurements at the Fe 2p excitation demonstrate that the ferrihydrite is bearing a mixed valence iron distribution. The stability of this uncommon phase is then discussed based on work previously reported in literature for analogous poorly ordered iron oxides. The specific biomineralization mechanism might be a key to the stabilization of this phase.