TY - JOUR

T1 - Electron flux is a key determinant of uranium isotope fractionation during bacterial reduction

AU - Brown, Ashley R.

AU - Molinas, Margaux

AU - Roebbert, Yvonne

AU - Sato, Ataru

AU - Abe, Minori

AU - Weyer, Stefan

AU - Bernier-Latmani, Rizlan

N1 - Funding Information: We thank Liang Shi for providing the recombinant MtrC S. oneidensis LS331 strain and Florence Pojer, Kelvin Lau and Amédé Larabi of the Protein Production and Structure Core Facility at EPFL for purification of MtrC. We also acknowledge Camila Morales for assistance with experiments and Prof. Masahiko Hada of Tokyo Metropolitan University for helpful discussions. Funding for this work was provided by an ERC consolidator grant awarded to R. Bernier-Latmani (725675: UNEARTH: “Uranium isotope fractionation: a novel biosignature to identify microbial metabolism on early Earth”). This work was also supported by JSPS KAKENHI Grant Numbers JP21H01864 and JP22J12551.

PY - 2023/9/19

Y1 - 2023/9/19

N2 - Uranium isotopic signatures in the rock record are utilized as a proxy for past redox conditions on Earth. However, these signatures display significant variability that complicates the interpretation of specific redox conditions. Using the model uranium-reducing bacterium, Shewanella oneidensis MR-1, we show that the abundance of electron donors (e.g., labile organic carbon) controls uranium isotope fractionation, such that high electron fluxes suppress fractionation. Further, by purifying a key uranium-reducing enzyme, MtrC, we show that the magnitude of fractionation is explicitly controlled by the protein redox state. Finally, using a mathematical framework, we demonstrate that these differences in fractionation arise from the propensity for back-reaction throughout the multi-step reduction of hexavalent uranium. To improve interpretations of observed fractionations in natural environments, these findings suggest that a variable intrinsic fractionation factor should be incorporated into models of uranium isotope systematics to account for differences in electron flux caused by organic carbon availability.

AB - Uranium isotopic signatures in the rock record are utilized as a proxy for past redox conditions on Earth. However, these signatures display significant variability that complicates the interpretation of specific redox conditions. Using the model uranium-reducing bacterium, Shewanella oneidensis MR-1, we show that the abundance of electron donors (e.g., labile organic carbon) controls uranium isotope fractionation, such that high electron fluxes suppress fractionation. Further, by purifying a key uranium-reducing enzyme, MtrC, we show that the magnitude of fractionation is explicitly controlled by the protein redox state. Finally, using a mathematical framework, we demonstrate that these differences in fractionation arise from the propensity for back-reaction throughout the multi-step reduction of hexavalent uranium. To improve interpretations of observed fractionations in natural environments, these findings suggest that a variable intrinsic fractionation factor should be incorporated into models of uranium isotope systematics to account for differences in electron flux caused by organic carbon availability.

UR - http://www.scopus.com/inward/record.url?scp=85171646656&partnerID=8YFLogxK

U2 - 10.1038/s43247-023-00989-x

DO - 10.1038/s43247-023-00989-x

M3 - Article

AN - SCOPUS:85171646656

VL - 4

JO - Communications Earth and Environment

JF - Communications Earth and Environment

M1 - 329

ER -