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James Byrne

The impact of trace metals on the microbial
reduction of Fe(III) minerals

    Iron is the fourth most abundant element in the Earth’s crust and can cycle between two principal redox states, the ferrous (+2) and ferric (+3) forms. Recent studies have shown that a diverse range of specialist microorganisms are able to conserve energy through the cycling of iron between these two oxidation states.  The oxidation of Fe (II) by acidophilic bacteria, first discovered in the 1950s, has been studied in some detail and has formed the basis of a lucrative global industry involved in “bioleaching” of precious metals from low grade ores.  The dissimilatory reduction of Fe (III) was a much more recent discovery, and also has major implications for the natural biogeochemical cycles of carbon, iron and other trace metals.  In many subsurface environments, Fe(III) reduction can also prove useful in the bioremediation of contaminated environments via the ability of Fe(III)-reducing bacteria to degrade organic contaminants and reduce toxic metals and metalloids (e.g. U(VI), Cr(VI), Tc(VII)) in lieu of Fe(III) or via indirect mechanisms.  In many examples, toxic transition metals and radionuclides can be incorporated into the structure of post reduction minerals such as magnetite, effectively locking up the metal for long-term disposal and even yielding novel bionanomaterials with unusual and exploitable properties.

The aim of this project is to combine classical microbiological techniques, with mineralogical and spectroscopic approaches to give a molecular-scale understanding of the mechanism of microbial Fe(III) reduction by Geobacter species, including information on the incorporation of potentially toxic trace metals into Fe(II)-bearing biomineral phases such as magnetite.  The impact of trace metal incorporation on the magnetic properties of the post reduction minerals will explored, alongside the stability of the biominerals and the potential to use the novel biominerals for a range of in situ and ex situ applications.