BioProject

The Materials Corrosion Test (MaCoTe) at the Underground Research Laboratory in Grimsel, Switzerland, assesses the microbiology and corrosion potential of engineered components of a deep geological repository (DGR) for long-term disposal of high-level nuclear waste. More...

The Materials Corrosion Test (MaCoTe) at the Underground Research Laboratory in Grimsel, Switzerland, assesses the microbiology and corrosion potential of engineered components of a deep geological repository (DGR) for long-term disposal of high-level nuclear waste. Diversity and temporal changes of bentonite-associated microbial profiles were assessed under DGR-like conditions in compacted Wyoming MX-80 bentonite (1.25 and 1.50 targeted dry densities) exposed to natural groundwater using culture-dependent and molecular techniques combining quantitative PCR, 16S rRNA gene sequencing and PLFA. Samples taken from the outside of the four-year borehole modules revealed up to 66% and 23% of 16S rRNA gene sequences affiliated with Desulfosporosinus and Desulfovibrio, respectively. Putatively involved in sulfate reduction, these ASVs were almost undetectable in the inner bentonite core. The microbial profiles of the inner bentonite core after one and four years of emplacement were similar to the uncompacted bentonite used to pack the borehole modules years earlier, revealing no detectable microbial growth. The number of culturable aerobic and anaerobic heterotrophic bacteria in the uncompacted bentonite were low, with less than 1000 and 100 colony forming units (CFUs) per g dry weight, respectively. Four years after emplacement, culturable heterotrophic bacterial CFUs and SRB did not change significantly inside the bentonite core. PLFA analysis detected a decrease of cell abundance estimates between MaCoTe bentonite samples emplaced for one as compared to four years. Culture-dependent and molecular approaches yielded complementary information on microbial communities in compacted bentonite. Together, our results provide strong evidence for microbial stability and inactivity inside highly compacted bentonite exposed to conditions that mimic engineered components of a deep geological repository. Less...