Microbial Characterization of Halite and Groundwater Samples from the WIPP
This report summarizes the progress made in characterizing the microbial community structures within the WIPP repository, and in surrounding groundwaters. Through cultivation and DNA-based identification, the potential activity of these organisms is being inferred, thus leading to a better understanding of their impact on WIPP performance. WIPP halite constitutes the near-field microbial environment. Microbial activity in this setting is predicted by WIPP performance assessment (PA) to proceed from aerobic respiration, through nitrate reduction, to focus on sulfate reduction. The role of methanogenesis in the WIPP remains unclear, due to both energetic constraints imposed by a high-salt environment and substrate selectivity, so this role is no longer considered in PA. Members of the three biological domains — Bacteria, Archaea, and Eukarya (in this case, Fungi) — have been found associated with WIPP halite. Thus far, their activity has been limited to aerobic respiration. Archaea identified in WIPP halite thus far fall exclusively within the family Halobacteriaceae. These include Halobacterium noricense, a Halorubrum-like species, and a Halopenitus-like species. Bacterial signatures associated with WIPP halite include members of the phylum Proteobacteria — Halomonas, Pelomonas, Limnobacter, and Chromohalobacter — but only the latter has been isolated. Also detected and cultivated were Salinicoccus and Nesterenkonia spp. Three fungal species were isolated from halite (Cladosporium, Phoma, and Engyodontium). Although these were most likely introduced into the WIPP as contaminants from above-ground, their survival and potential role in the WIPP (e.g., cellulose degradation) is under investigation. WIPP groundwaters comprise the far-field microbial environment. Bacteria cultivated and identified from the overlying Culebra and nearby borehole groundwater are capable of aerobic respiration, denitrification, fermentation, metal reduction, and sulfate reduction, and are distributed across many different phyla. Their structural and metabolic diversity is dependent upon the ionic strength of the sampled groundwater, with a decrease in both at higher strength. Two of the Bacteria found in groundwater were also found in WIPP halite (Chromohalobacter sp. and Virgibacillus sp.). Archaea identified in groundwater include Halococcus saccharolyticus, Haloferax sp., and Natrinema sp. The differences in the microbial communities detected thus far in halite and groundwater suggest that there will be significant differences in the associated metabolic potential of the near- and far-field environments. Whereas the near-field is dominated by Archaea with more limited metabolic capabilities, the far-field is dominated by Bacteria with extremely broad capabilities. The authors wish to thank Russ Patterson and Dan Ferguson (DOE-CBFO) for their support, and Washington TRU Solutions for access to sampling. All research was performed by the Los Alamos National Laboratory Actinide Chemistry & Repository Science team at the Carlsbad Environmental and Monitoring Research Center, managed by New Mexico State University (NMSU) and located in Carlsbad, NM. Funding for this research is through the Waste Isolation Pilot Plant project, managed by the Department of Energy—Carlsbad Field Office.