Biomineralization of a poorly crystalline Fe(III) oxide, akaganeite, by an anaerobic Fe(III)-reducing bacterium (Shewanella alga) isolated from marine environment

Formation of Fe(II)-containing mineral through microbial processes may play an important role in iron and carbon geochemistry in subsurface environments. Fe(III)-reducing bacteria form Fe(II)-containing minerals such as siderite, magnetive, vivianite, and green rust using iron oxides. A psychrotolerant Fe(III)-reducing bacterium,Shewanella alga (PV-4), was used to examine the reduction and biomineralization of a poorly crystalline iron oxide, akaganeite (β-FeOOH), in the absence of a soluble electron shuttle, anthraquinone disulphonate (AQDS), under different atmospheric compositions as well as in HCO3− buffered medium (30 to 210 mM). Iron biomineralization was also examined under different growth conditions such as incubation time, electron donors, and electron acceptors. The Fe(III)-reducing bacterium, PV-4, reduced akaganeite, Fe(III)-citrate, and Co(III)-EDTA using lactate or H2 as an electron donor. The iron biomineralization of Fe(III) oxide, akaganeite—as it undergos reduction by an iron reducing bacterium—is a complex process influenced by biogeochemical factors including microorganisms, bicarbonate buffer concentration, atmospheric composition, electron donors/acceptors, incubation time, and Eh/pH. From this research we found that microorganisms do participate in the formation of diverse iron minerals and that microbial iron biomineralization may affect Fe and C biogeochemistry in subsurface environments.