We experimentally determined the magnitude of uranium isotopic fractionation induced by U(VI) reduction by metal reducing bacterial isolates. Our results indicate that microbial U(VI) reduction induces isotopic fractionation; heavier isotopes (i.e., 238U) partition into the solid U(IV) products. The magnitudes of isotopic fractionation (expressed as ε=1000‰*(α-1)) for 238U/235U were 0.68‰±0.05‰v and 0.99‰ ±0.12‰ for Geobacter sulfurreducens strain PCA and strain IFRC-N, respectively. The ε values for Anaeromyxobacter dehalogenans strain FRC-W, strain FRC-R5, a novel Shewanella isolate, and Desulfitobacterium sp. strain Viet1 were 0.72‰ ±0.15‰, 0.99‰±0.12‰, 0.96‰ ±0.16‰ and 0.86‰±0.06‰, respectively. Our results show that the maximum ε values of ~1.0‰ were obtained with low biomass (~107cells/mL) and low electron donor concentrations (~500μM). These results provide an initial assessment of 238U/235U shifts induced by microbially-mediated U(VI) reduction, which is needed as 238U/235U data are increasingly applied as redox indicators in various geochemical settings.
ASJC Scopus subject areas
- Geochemistry and Petrology