The isotopic signature of U^V during bacterial reduction

authored by

A. R. Brown, M. Molinas, Y. Roebbert, R. Faizova, T. Vitova, A. Sato, M. Hada, M. Abe, M. Mazzanti, S. Weyer, R. Bernier-Latmani

Abstract

The two step electron transfer during bacterial reduction of U^VI to U^IV is typically accompanied by mass-independent fractionation of the ²³⁸U and ²³⁵U isotopes, whereby the heavy isotope accumulates in the reduced product. However, the role of the U^V intermediate in the fractionation mechanism is unresolved due to the challenges associated with its chemical stability. Here, we employed the U^V stabilising ligand, dpaea^2-, to trap aqueous U^V during U^VI reduction by Shewanella oneidensis. Whilst the first reduction step from U^VI to U^V displayed negligible fractionation, reduction of U^V to U^IV revealed mass-dependent isotope fractionation (preferential reduction of the ²³⁵U), contrary to most previous observations. This surprising behaviour highlights the control that the U-coordinating ligand exerts over the balance between reactant U supply, electron transfer rate, and U^IV product sequestration, suggesting that U^V speciation should be considered when using U isotope ratios to reconstruct environmental redox conditions.

Organisation(s)

Institute of Mineralogy
Geochemistry

External Organisation(s)

École polytechnique fédérale de Lausanne (EPFL)
Karlsruhe Institute of Technology (KIT)
Tokyo Metropolitan University
Hiroshima University

Type

Article

Journal

Geochemical Perspectives Letters

Volume

29

Pages

45-50

No. of pages

6

ISSN

2410-339X

Publication date

09.04.2024

Publication status

Published

Peer reviewed

Yes

ASJC Scopus subject areas

Environmental Chemistry, Geology, Geochemistry and Petrology

Electronic version(s)

https://doi.org/10.7185/geochemlet.2411 (Access: Open)