Reductive Dehalogenation of Trichloromethane by Two Different <i>Dehalobacter restrictus</i> Strains Reveal Opposing Dual Element Isotope Effects
Bibliographic record
Abstract
Trichloromethane (TCM) is a frequently detected and persistent groundwater contaminant. Recent studies have reported that two closely related Dehalobacter strains (UNSWDHB and CF) transform TCM to dichloromethane, with inconsistent carbon isotope effects (ε 13 C UNSWDHB = −4.3 ± 0.45‰; ε 13 C CF = −27.5 ± 0.9‰). This study uses dual element compound specific isotope analysis (C; Cl) to explore the underlying differences. TCM transformation experiments using strain CF revealed pronounced normal carbon and chlorine isotope effects (ε 13 C CF = −27.9 ± 1.7‰; ε 37 Cl CF = −4.2 ± 0.2‰). In contrast, small carbon and unprecedented inverse chlorine isotope effects were observed for strain UNSWDHB (ε 13 C UNSWDHB = −3.1 ± 0.5‰; ε 37 Cl UNSWDHB = 2.5 ± 0.3‰) leading to opposing dual element isotope slopes (λ CF = 6.64 ± 0.14 vs λ UNSWDHB = −1.20 ± 0.18). Isotope effects of strain CF were identical to experiments with TCM and Vitamin B 12 (ε 13 C Vitamin B12 = −26.0 ± 0.9‰, ε 37 Cl Vitamin B12 = −4.0 ± 0.2‰, λ Vitamin B12 = 6.46 ± 0.20). Comparison to previously reported isotope effects suggests outer-sphere-single-electron transfer or S N 2 as possible underlying mechanisms. Cell suspension and cell free extract experiments with strain UNSWDHB were both unable to unmask the intrinsic KIE of the reductive dehalogenase (TmrA) suggesting that enzyme binding and/or mass-transfer into the periplasm were rate-limiting. Nondirected intermolecular interactions of TCM with cellular material were ruled out as reason for the inverse isotope effect by gas/water and gas/hexadecane partitioning experiments indicating specific, yet uncharacterized interactions must be operating prior to catalysis.
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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 | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| 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".