FIG 2.

Microbial community composition of borehole module samples after 13 months of exposure. A mixture of pellets and powdered bentonite was used to prepare borehole modules 1A (gray circles) and 2A (black circles) at dry densities of 1.25 and 1.50 gm/cm³, respectively. After assembly, the bentonite was fully saturated using pore water extracted from borehole 13.001, and modules were placed in borehole at the Grimsel URL in Switzerland. After 394 days of exposure, the modules were retrieved and analyzed. Samples are sorted from left to right by location within the module, from outside to inside. Results of two replicate DNA extractions (a and b) using the PowerSoil DNA isolation kit or PowerMax DNA isolation kit are shown. No replicates are shown for samples 4, 7, 14, and 17. *, samples that were amplified using primer 515F-Y/926R. All other samples were amplified using Pro341F/Pro805R. Relative abundances of microbial taxa (≥6% abundance) are shown. Colors correspond to taxa that are discussed in the text.