Sustained dechlorination of vinyl chloride to ethene in <i>Dehalococcoides</i> -enriched cultures grown without addition of exogenous vitamins and at low pH
Bibliographic record
Abstract
ABSTRACT Trichloroethene (TCE) is a ubiquitous groundwater pollutant. Successful TCE bioremediation has been demonstrated at field sites using specialized microbial consortia harboring TCE-respiring Dehaloccocoides whose growth is cobalamin (vitamin B 12 )-dependent. Bioaugmentation cultures grown ex situ with ample exogenous vitamins in the medium and at neutral pH may become vitamin-limited or inhibited by acidic pH once injected into field sites, resulting in incomplete TCE dechlorination and accumulation of more toxic vinyl chloride (VC). Here, we report growth of the Dehalococcoides -containing bioaugmentation culture KB-1 in a TCE-amended mineral medium devoid of vitamins and in a VC-amended mineral medium at low pH (6.0 and 5.5). In cultures grown without exogenous vitamins or cobalamin, Acetobacterium , which can synthesize 5,6-dimethylbenzimidazole (DMB), the lower ligand of cobalamin, and Sporomusa are the dominant acetogens. At neutral pH, a growing Acetobacterium population supports complete TCE dechlorination by Dehalococcoides at millimolar levels with a substantial increase in the amount of measured cobalamin (~20-fold). Sustained dechlorination of VC to ethene was achieved at a pH as low as 5.5, yet at low pH Acetobacterium is less abundant, potentially affecting the production of DMB and/or cobalamin. However, dechlorination activity at very low pH (< 5.0) was not stimulated by DMB supplementation, but was restored by raising pH to neutral. Assays in cell extracts revealed that vinyl chloride reductase (VcrA) activity declines significantly below pH 6.0 and is undetectable below pH 5.0. This study highlights the roles of and interplay between vitamin-producing populations and pH in microbial dechlorinating communities, and their importance for successful chlorinated ethenes bioremediation at field sites.
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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 | 0.000 | 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".