Methanogenic biodegradation of cyclohexane by microbial consortia from oil sands tailings
Bibliographic record
Abstract
Cyclohexane, a significant component of light oils and some refined fuels, can be introduced into the environment through petroleum production and fuel spills; it is also present in tailings from certain surface-mined oil sands ores. The environmental fate of cyclohexane is cryptic in oxygen-depleted methanogenic environments. Indigenous microorganisms in primary oil sands tailings cultures and cyclohexane-adapted- d 12 enrichments were used to test methanogenic biodegradation of 1 mM cyclohexane alone or with the potential co-substrate n -heptane in a 70:30 mixture. We assessed substrate depletion, metabolite production, methane accumulation, and changes in microbial community composition during incubation. Cyclohexane was depleted slowly but completely in primary cultures during 260 d when added alone or with n -heptane, and more quickly in enrichment cultures during 120 d incubation, yielding ∼66–75 % of theoretical maximum methane production. Analysis of derivatized extracts from cultures grown with unlabelled or fully deuterated cyclohexane‑ d 12 revealed fragment ions of m/z 329 and m/z 341 characteristic of cyclohexylsuccinic acid, the first intermediate in a fumarate addition pathway. Members of the bacterial and archaeal families Desulfotomaculaceae (previously classified in Peptococcaceae ), Methanosaetaceae , and Methanoregulaceae were associated with cyclohexane degradation. A major shift in Desulfotomaculaceae abundance (7.2 % of the total community) occurred with cyclohexane‑ d 12 enrichment by d 120, indicating a significant role in biodegradation. Additional contributions from Syntrophaceae and Coriobacteriaceae were observed in n -heptane degradation. This report of cyclohexane biodegradation under methanogenic conditions, likely via fumarate addition, provides insight into the fate of resistant compounds in hydrocarbon-impacted sites and helps predict greenhouse gas emissions from oil-contaminated methanogenic environments.
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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) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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".