BG Biogeosciences BG 1726-4189 Copernicus GmbH Göttingen, Germany 10.5194/bg-9-1033-2012 Integrative analysis of <i>Geobacter</i> spp. and sulfate-reducing bacteria during uranium bioremediation Barlett M. 1 3 Zhuang K. 2 3 Mahadevan R. 2 Lovley D. 1 Department of Microbiology, Morrill Science Center IV North, University of Massachusetts, 639 North Pleasant St., Amherst, MA, 01003-9298, USA Department of Chemical Engineering and Applied Chemistry, University of Toronto, 200 College St. Rm 326, Toronto, ON, M5S 3E5, Canada These authors contributed equally to this work. 16 03 2012 9 3 1033 1040 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.biogeosciences.net/9/1033/2012/bg-9-1033-2012.html The full text article is available as a PDF file from http://www.biogeosciences.net/9/1033/2012/bg-9-1033-2012.pdf

Enhancing microbial U(VI) reduction with the addition of organic electron donors is a promising strategy for immobilizing uranium in contaminated groundwaters, but has yet to be optimized because of a poor understanding of the factors controlling the growth of various microbial communities during bioremediation. In previous field trials in which acetate was added to the subsurface, there were two distinct phases: an initial phase in which acetate-oxidizing, U(VI)-reducing <i>Geobacter</i> predominated and U(VI) was effectively reduced and a second phase in which acetate-oxidizing sulfate reducing bacteria (SRB) predominated and U(VI) reduction was poor. The interaction of <i>Geobacter</i> and SRB was investigated both in sediment incubations that mimicked in situ bioremediation and with in silico metabolic modeling. In sediment incubations, <i>Geobacter</i> grew quickly but then declined in numbers as the microbially reducible Fe(III) was depleted whereas the SRB grow more slowly and reached dominance after 30–40 days. Modeling predicted a similar outcome. Additional modeling in which the relative initial percentages of the <i>Geobacter</i> and SRB were varied indicated that there was little to no competitive interaction between <i>Geobacter</i> and SRB when acetate was abundant. Further simulations suggested that the addition of Fe(III) would revive the <i>Geobacter</i>, but have little to no effect on the SRB. This result was confirmed experimentally. The results demonstrate that it is possible to predict the impact of amendments on important components of the subsurface microbial community during groundwater bioremediation. The finding that Fe(III) availability, rather than competition with SRB, is the key factor limiting the activity of <i>Geobacter</i> during in situ uranium bioremediation will aid in the design of improved uranium bioremediation strategies.

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