Microbial Community Analysis of Opalinus Clay Drill Core Samples from the Mont Terri Underground research Laboratory, Switzerland

Opalinus Clay is a candidate host rock for a high-level radioactive waste repository in Switzerland. Microbial metabolism and its by-products could affect the physical and (geo)chemical conditions in such a repository. This study investigated the occurrence of indigenous microbes, their community size and-structure in an Opalinus Clay core from the Mont Terri Underground Research Laboratory, Switzerland, drilled with aseptic techniques. Core sub-samples were distributed to five laboratories, where they were analysed with microscopy, culture-and molecular biology techniques. Evidence supporting a viable microbial community in Opalinus Clay included: five positive culture results (including for sulphate-reducing bacteria, SRB) out of 20 culture attempts; extraction of 64 ng phospholipid fatty acids (PLFA) per g clay, suggesting the presence of viable cells; detection of PLFA biomarkers for anaerobic Gram-negative bacteria and SRB; and the presence of sufficient nutrients to support growth of indigenous and ...