Deciphering indigenous bacteria in compacted bentonite through a novel and efficient DNA extraction method: Insights into biogeochemical processes within the Deep Geological Disposal of nuclear waste concept

Compacted bentonites are one of the best sealing and backfilling clays considered for use in Deep Geological Repositories radioactive wastes. However, an in-depth understanding their behavior after placement repository is required, including if activity indigenous microorganisms affects safety conditions. Here we provide optimized phenol:chloroform based protocol that facilitates higher DNA-yields when other methods failed. To demonstrate efficiency this method, DNA was extracted from acetate-treated compacted at 1.5 1.7 g/cm 3 densities 24 months anoxic incubation. Among 16S rRNA gene sequences identified, those most similar to taxa mediating biogeochemical sulfur cycling included oxidizing (e.g., Thiobacillus, Sulfurimonas ) sulfate reducing Desulfuromonas Desulfosporosinus bacteria. In addition, iron-cycling populations iron Thiobacillus Rhodobacter plus Geobacillus ). Genera described capacity utilize acetate as a carbon source were also detected such Delftia Stenotrophomonas . Lastly, microscopic analyses revealed pores cracks could host nanobacteria or spores. This study highlights potential role microbial driven processes effect high compaction on diversity Repositories. • Optimization effective extraction method highly bentonites. Pores bentonite showed by analyses. High bacterial identified specimens up dry density. Bacteria S Fe cycles enriched acetate. No significant differences marked 2-years period.