title: Uranium isotopes fingerprint biotic reduction.
abstract: Knowledge of paleo-redox conditions in the Earth's history provides a window into events that shaped the evolution of life on our planet. The role of microbial activity in paleo-redox processes remains unexplored due to the inability to discriminate biotic from abiotic redox transformations in the rock record. The ability to deconvolute these two processes would provide a means to identify environmental niches in which microbial activity was prevalent at a specific time in paleo-history and to correlate specific biogeochemical events with the corresponding microbial metabolism. Here, we demonstrate that the isotopic signature associated with microbial reduction of hexavalent uranium (U), i.e., the accumulation of the heavy isotope in the U(IV) phase, is readily distinguishable from that generated by abiotic uranium reduction in laboratory experiments. Thus, isotope signatures preserved in the geologic record through the reductive precipitation of uranium may provide the sought-after tool to probe for biotic processes. Because uranium is a common element in the Earth's crust and a wide variety of metabolic groups of microorganisms catalyze the biological reduction of U(VI), this tool is applicable to a multiplicity of geological epochs and terrestrial environments. The findings of this study indicate that biological activity contributed to the formation of many authigenic U deposits, including sandstone U deposits of various ages, as well as modern, Cretaceous, and Archean black shales. Additionally, engineered bioremediation activities also exhibit a biotic signature, suggesting that, although multiple pathways may be involved in the reduction, direct enzymatic reduction contributes substantially to the immobilization of uranium.
authors.affiliation: Environmental Microbiology Laboratory, École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland;
authors.forename: Malgorzata
authors.initials: M
authors.lastname: Stylo
authors.affiliation: Institut für Mineralogie, Leibniz Universitat Hannover, D-30167 Hannover, Germany; and.
authors.forename: Nadja
authors.initials: N
authors.lastname: Neubert
authors.affiliation: Environmental Microbiology Laboratory, École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland;
authors.forename: Yuheng
authors.initials: Y
authors.lastname: Wang
authors.affiliation: School of Earth and Space Exploration, Arizona State University, 85287 Tempe, AZ.
authors.forename: Nikhil
authors.initials: N
authors.lastname: Monga
authors.affiliation: School of Earth and Space Exploration, Arizona State University, 85287 Tempe, AZ.
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Romaniello
authors.affiliation: Institut für Mineralogie, Leibniz Universitat Hannover, D-30167 Hannover, Germany; and.
authors.forename: Stefan
authors.initials: S
authors.lastname: Weyer
authors.affiliation: Environmental Microbiology Laboratory, École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland; rizlan.bernier-latmani@epfl.ch.
authors.forename: Rizlan
authors.initials: R
authors.lastname: Bernier-Latmani
mesh_terms: D001673:Biodegradation, Environmental; D004463:Ecology / Q000379:methods; D019015:Geologic Sediments / Q000737:chemistry* / Q000382:microbiology*; D055593:Geological Phenomena; D008855:Microscopy, Electron, Scanning; D010084:Oxidation-Reduction; D010163:Paleontology / Q000379:methods; D015203:Reproducibility of Results; D020592:Shewanella / Q000378:metabolism*; D014501:Uranium / Q000032:analysis* / Q000378:metabolism; D056928:X-Ray Absorption Spectroscopy
chemical_list: D014501:Uranium
keywords: bioremediation; biosignature; isotopes; paleoredox; uranium