Microbial diversity and activity in permafrost and ground ice from the Canadian High Arctic
Bibliographic record
Abstract
We have developed methods to obtain pristine permafrost/ground ice samples from the Canadian high Arctic and demonstrated that these methods are suitable for both culture-dependent and culture-independent microbiological analyses. In an initial study, the culturable microbial community in a 9 m deep permafrost sample was dominated by spore-forming genera of Bacteria from the phylum Firmicutes while the phyla Actinobacteria and Proteobacteria were also represented. Phenotypic characterization of the isolates indicated a predominantly psychrotolerant and halotolerant microbial community. A culture-independent survey of the microbial diversity in this sample revealed higher diversity, as Bacteria from 6 phyla (Actinobacteria, CFB, Firmicutes, Gemmatimonadetes, Planctomyces , and Proteobacteria) and both of the major Archaea phyla (Euryarchaeota and Crenarchaeota ) were identified. Differences in the abundance, diversity, and activity of the microbial communities in distinct horizons of a permafrost/ground ice core were investigated using a combination of culture-independent methods, aerobic plate counts and a novel method for detecting microbial activity at subzero temperatures, developed during this thesis. The active layer, permafrost table, and permafrost horizons showed similar microbial abundance and diversity. The microbial community in ground ice was less abundant and diverse. The culturable microbial community from the active layer was composed of Bacteria related to the Proteobacteria, Actinobacteria, CFB, and Firmicutes while all of the isolates from the permafrost were related to spore-forming Firmicutes. No viable cells were recovered from the ground ice. Microbial activity was detected in all of the Eur3 horizons, including low levels of activity at near ambient subzero permafrost temperatures. Many of the isolates from the permafrost had low 16S rRNA gene sequence similarity to characterized species. A polyphasic characterization of one of these potentially unique isolates was undertaken to better define its taxonomy. The isolate (Eur1 9.5) was differentiated from related species based on its morphology, fatty acid profile and growth characteristics and represents the type species of a new genus, namely Tumebacillus permanentifrigoris . This work demonstrates that Canadian high Arctic permafrost is a unique environment that harbors a diverse microbial community with members capable of activity at near in situ temperatures. In comparison, ground ice is a relatively inhospitable environment and supports low microbial abundance, diversity and activity.
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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 | 0.002 | 0.002 |
| Science and technology studies | 0.002 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 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".