Oxidative biotransformation of biotite and glauconite by alkaliphilic anaerobes: The effect of Fe oxidation on the weathering of phyllosilicates

Two alkaliphilic anaerobic bacteria, namely, the dissimilatory iron-reducer Geoalkalibacter ferrihydriticus and the fermentative hydrolytic Clostridium alkalicellulosi, along with their co-cultures, are studied to examine their ability to release Si and Fe from two main Fe-containing phyllosilicates in Earth's crust: biotite and glauconite. The formation of magnetically ordered phase(s) within 200 days of incubation was only observed in the presence of G. ferrihydriticus whether in a mono- or co-culture but not in the abiotic controls or a pure culture of C. alkalicellulosi. The co-culture of these organisms could represent a simple trophic chain in which C. alkalicellulosi decomposed microcrystalline cellulose to produce organic acids and ethanol, while G. ferrihydriticus, as we expected, utilized these products and reduces Fe(III) in phyllosilicate lattices. Unexpectedly, G. ferrihydriticus did not utilize but instead produced an additional 3 mM of acetate during growth with phyllosilicates. An analysis of the Mossbauer spectra of biotite and glauconite that were weathered in the presence of G. ferrihydriticus revealed magnetically ordered phases that formed by Fe2+ oxidation rather than by Fe3+ reduction. The only possible explanation of this phenomenon could be in the ability of G. ferrihydriticus to produce acetate during anaerobic Fe2+ oxidation with carbonate as an electron acceptor. Thermodynamic calculations show the possibility of such a reaction. Thus, microorganisms with respiratory metabolism could play an active role in the bioweathering of phyllosilicates under alkaline anaerobic conditions. The bacterial anaerobic oxidation of ferrous iron with carbonate as an electron donor is supposed to have played a significant role in ancient environments, serving as one of the causes of banded iron formations. (C) 2016 Elsevier B.V. All rights reserved.