Mechanistic Dichotomy in Bacterial Trichloroethene Dechlorination Revealed by Carbon and Chlorine Isotope Effects
Bibliographic record
Abstract
Tetrachloroethene (PCE) and trichloroethene (TCE) are significant groundwater contaminants. Microbial reductive dehalogenation at contaminated sites can produce nontoxic ethene but often stops at toxic cis -1,2-dichloroethene ( cis -DCE) or vinyl chloride (VC). The magnitude of carbon relative to chlorine isotope effects (as expressed by Λ C/Cl, the slope of δ 13 C versus δ 37 Cl regressions) was recently recognized to reveal different reduction mechanisms with vitamin B 12 as a model reactant for reductive dehalogenase activity. Large Λ C/Cl values for cis -DCE reflected cob(I)alamin addition followed by protonation, whereas smaller Λ C/Cl values for PCE evidenced cob(I)alamin addition followed by Cl – elimination. This study addressed dehalogenation in actual microorganisms and observed identical large Λ C/Cl values for cis -DCE (Λ C/Cl = 10.0 to 17.8) that contrasted with identical smaller Λ C/Cl for TCE and PCE (Λ C/Cl = 2.3 to 3.8). For TCE, the trend of small Λ C/Cl could even be reversed when mixed cultures were precultivated on VC or DCEs and subsequently confronted with TCE (Λ C/Cl = 9.0 to 18.2). This observation provides explicit evidence that substrate adaptation must have selected for reductive dehalogenases with different mechanistic motifs. The patterns of Λ C/Cl are consistent with practically all studies published to date, while the difference in reaction mechanisms offers a potential answer to the long-standing question of why bioremediation frequently stalls at cis -DCE.
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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 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| 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".