The interplay between microbial metabolism and survival at surface-air interfaces : Implications for the Long-Term Storage of Used Nuclear Fuel
Bibliographic record
Abstract
The Nuclear Waste Management Organization of Canada was mandated with the safe, long-term containment of the mounting nuclear industry waste (NWMO, 2005). The engineering of a multi-level barrier system in deep geological repositories to prevent radionuclide escape into groundwater involves the multidisciplinary collaboration of physicists, modelers, engineers, policy makers and legislators. This extreme environment is largely inhospitable to life nevertheless microbial ubiquity demands biological attention if we are to approach risk assessment with legislative integrity. Two decades of work driven by an engineer-turnedmicrobiologist (Stroes-Gascoyne et al., 2010) provided extensive data to support highly compacted bentonite clay for microbial suppression during repository saturation. However, interfaces still demand microbiological attention (Wolfaardt and Korber, 2012), and desiccated bentonite interfaces are thus the focus of this research. The foundational work (Chapter 2) developed tools for evaluating microbial activity in saturated and desiccated bentonite. Novel aspects included the evaluation of precipitated sulphides with fluorometry, and the use of closed loop CO2 measurements to assess microbial metabolism at bentonite-air interfaces. These tools were employed (Chapter 3) to measure the influence of relative humidity (RH) on persistent microbial metabolic activity at bentonite-air interfaces, and the influence of metabolic activity on the clay matrix. It was shown that the combination of bentonite interfaces and high RH stimulated the metabolic persistence of microbial communities during desiccation, despite high RH inhibiting the long-term survival of viable communities. A number of hypotheses were built on these observations (Chapter 4). These extended the observation of the interactive influence of high RH and bentonite to another hygroscopic matrix, polyethylene glycol, confirming that hygroscopic interfaces and high RH improve microbial access to water vapor at surface-air interfaces. It was also shown that oligotrophy increases biofilm desiccation-resilience in a desiccation-tolerant species (Arthrobacter), but not a desiccation-sensitive species (Pseudomonas). An appreciation of the microbial ability to harness their matrix for access to water vapor, and the interaction of this metabolic persistence with long-term survival, is applicable in the modeling and engineering of these industrial environments, and is an intriguing picture of the response of these versatile organisms to the vast challenges within which they so remarkably persist.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.002 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".