Niche Partitioning of Microbial Communities at an Ancient Vitrified Hillfort: Implications for Vitrified Radioactive Waste Disposal

• Published in: Geomicrobiology journal Vol. 38; no. 1
• Main Authors: Plymale, Andrew E., Wells, Jacqueline R., Pearce, Carolyn I., Brislawn, Colin J., Graham, Emily B., Cheeke, Tanya E., Allen, Jessica L., Fansler, Sarah J., Arey, Bruce W., Bowden, Mark E., Saunders, Danielle L., Danna, Vincent G., Tyrrell, Kimberly J., Weaver, Jamie L., Sjöblom, Rolf, Paul, Rick, McCloy, John S., Hjärthner-Holdar, Eva, Englund, Mia, Ogenhall, Erik, Peeler, David K., Kruger, Albert A.
• Format: Journal Article
• Language: English
• Published: United States Taylor & Francis 31-08-2020
• Subjects: BASIC BIOLOGICAL SCIENCES; community structure; habitat analogue; microbes and surfaces; molecular ecology; near surface radioactive waste disposal
• ISSN: 0149-0451; 1521-0529

A pre-Viking era vitrified hillfort, Broborg, provides a habitat analogue for disposed radioactive waste glass and shows strong niche partitioning among the organisms involved in glass alteration. Microbes cannot be eliminated from radioactive waste disposal facilities and the consequences of bio-colonization must be understood. We use Broborg as a model system to inform what microbial processes might influence long-term radioactive waste glass durability by examining anthropogenic glass that has been subjected to bio-colonization for over 1,500 years. Scanning electron microscopy (SEM) images reveal the surficial biofilm structure, and chemical/mineralogy analysis in combination with deoxyribonucleic acid (DNA) sequencing of samples from the vitrified substrate, the adjacent soil, and the general topsoil provide insight into niche partitioning. The ancient glass niche supports a unique microbial community of bacteria, fungi, and protists that manifests the species response to local geochemical and mineralogical conditions. Communities from the geochemical niche associated with the glass are distinct and less diverse than soil communities. The microbiome of the glass and adjacent soil are dominated by lichens, lichen-associated microorganisms, and other epilithic, endolithic, and epigeic organisms. Pseudomonads dominate the prokaryotic communities on the vitrified material, but not the adjacent soil. In contrast, the general topsoil communities are enriched in plant rhizosphere organisms. Taxa associated with vitrification have bio-corrosive properties that could be detrimental to glass durability, including silicate mineral dissolution, extraction of essential elements, secretion of geochemically reactive organic acids, and dissolution induced by improved water retention. However, these stable long-term biofilms also possess a homeostatic function that could limit glass alteration. Overall, this study demonstrates the potential impacts that microbial colonization and niche partitioning can have on glass alteration and subsequent release of radionuclides from a disposal facility for vitrified radioactive waste.