Long-term tracking of the microbiology of uranium-amended water-saturated bentonite microcosms: A mechanistic characterization of U speciation Morales Hidalgo, Mar Povedano Priego, Cristina Martinez-Moreno, Marcos F. Ojeda, Jesus J. Jroundi, Fadwa Merroun, Mohamed Larbi DGR Bentonite slurry Uranium Long-term incubation Microbial diversity Sulfate-reducing bacteria Deep geological repositories (DGRs) stand out as one of the optimal options for managing high-level radioactive waste (HLW) such as uranium (U) in the near future. Here, we provide novel insights into microbial behavior in the DGR bentonite barrier, addressing potential worst-case scenarios such as waste leakage (e.g., U) and groundwater infiltration of electron rich donors in the bentonite. After a three-year anaerobic incubation, Illumina sequencing results revealed a bacterial diversity dominated by anaerobic and spore-forming microorganisms mainly from the phylum Firmicutes. Highly U tolerant and viable bacterial isolates from the genera Peribacillus, Bacillus, and some SRB such as Desulfovibrio and Desulfosporosinus, were enriched from U-amended bentonite. The results obtained by XPS and XRD showed that U was present as U(VI) and as U(IV) species. Regarding U(VI), we have identified biogenic U(VI) phosphates, U(UO2)·(PO4)2, located in the inner part of the bacterial cell membranes in addition to U(VI)-adsorbed to clays such as montmorillonite. Biogenic U(IV) species as uraninite may be produced as result of bacterial enzymatic U(VI) reduction. These findings suggest that under electron donor-rich water-saturation conditions, bentonite microbial community can control U speciation, immobilizing it, and thus enhancing future DGR safety if container rupture and waste leakage occurs. 2024-07-10T10:53:45Z 2024-07-10T10:53:45Z 2024-06-26 journal article Morales-Hidalgo, M., Povedano-Priego, C., Martinez-Moreno, M. F., Ojeda, J. J., Jroundi, F., & Merroun, M. L. (2024). Long-term tracking of the microbiology of uranium-amended water-saturated bentonite microcosms: a mechanistic characterization of U speciation. Journal of Hazardous Materials, 135044. https://hdl.handle.net/10481/93058 https://doi.org/10.1016/j.jhazmat.2024.135044 eng info:eu-repo/grantAgreement/EC/H2020/847593 http://creativecommons.org/licenses/by-nc-nd/4.0/ open access Attribution-NonCommercial-NoDerivatives 4.0 Internacional Elsevier