SREL Reprint #2778

Iron reduction and alteration of nontronite NAu-2 by a sulfate-reducing bacterium

Yi-Liang Li1, Hojatollah Vali2,3, S. Kelly Sears3, John Yang4, Baolin Deng5, and Chuanlun L. Zhang1

1Savannah River Ecology Laboratory, University of Georgia, Aiken, South Carolina 29803, USA
2Department of Anatomy and Cell Biology/Department of Earth and Planetary Sciences, McGill University, Montreal, Quebec H3A 2B2 Canada
3Facility for Electron Microscopy Research, McGill University, Montreal, Quebec H3A 2B2 Canada
4Center for Environmental Sciences, Lincoln University, Jefferson City, Missouri 65201, USA
SDepartment of Civil & Environmental Engineering, University of Missouri, Columbia, Missouri 65211, USA

Abstract: Iron-rich clay minerals are abundant in the natural environment and are an important source of iron for microbial metabolism. The objective of this study was to understand the mechanism(s) of enhanced reduction of Fe(III) in iron-rich 2:1 clay minerals under sulfate-reducing conditions. In particular, biogenic reduction of structural Fe(III) in nontronite NAu-2, an Fe-rich smectite-group mineral, was studied using a Desulfovibrio spp. strain G-11 with or without amended sulfate. The microbial production of Fe(II) from NAu-2 is about 10% of total structural Fe(III) (30 mM) when Fe(III) is available as the sole electron acceptor. The measured production of Fe(II), however, can reach 29% of the total structural Fe(III) during sulfate reduction by G-11 when sulfate (50 mM) is concurrently added with NAu-2. In contrast, abiotic production of Fe(II) from the reaction of NAu-2 with Na2S (50 mM) is only ca. 7.5% of the total structural Fe(III). The enhanced reduction of structural Fe(III) by G-11, particularly in the presence of sulfate, is closely related to the growth rate and metabolic activities of the bacteria. Analyses by X-ray diffraction, transmission electron microscopy, and energy dispersive spectroscopy reveal significant changes in the structure and composition of NAu-2 during its alteration by bacterial sulfate reduction. G-11 can also derive nutrients from NAu-2 to support its growth in the absence of amended minerals and vitamins. Results of this study suggest that sulfate-reducing bacteria may play a more significant role than previously recognized in the cycling of Fe, S, and other elements during alteration of Fe-rich 2:1 clay minerals and other silicate minerals.

SREL Reprint #2778

Li, Y., H. Vali, S. K. Sears, J. Yang, B. Deng, and C. L. Zhang. 2004. Iron reduction and alteration of nontronite NAu-2 by a sulfate-reducing bacterium. Geochimica et Cosmochimica Acta 68:3251-3260.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).