Many iron-depositing microorganisms make distinctive iron mineralized filaments, which form iron mats in oxic-anoxic transition zones (e.g. in wetlands and deep-sea hydrothermal vents).  Iron-depositing microbes have likely been significant biogeochemical agents throughout Earth's history, possibly contributing to banded iron formations. We can use Fe microfossils to constrain paleoenvironmental chemistry if we link biomineral morphologies to microbial physiology and growth conditions. We investigated growth and biomineralization by the marine Mariprofundus ferrooxydans PV-1, as well as Leptothrix-like organisms from a freshwater iron seep.  Microbes were grown in chambers that were observed by light and confocal microscopy. This was coupled with solid-state electrode voltammetry to pair imaging with in situ measurements of Fe(II), Fe(III), Mn(II), and O2 gradients. Iron filaments were deposited under low oxygen concentrations and showed distinct morphologies and directionality similar to iron microfossils.  Our results can be used to interpret products of microaerophilic iron-depositing microbial activity in ancient environments.

Combining microscopy and voltammetry to link Fe biomineralization with geochemical conditions

245th National Meeting (2013)

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