Bibliographic record
Abstract
This dissertation describes several studies of anaerobic benzene degradation by microorganisms and fulfills four objectives. The first and second objectives were to characterize microbial populations in two benzene-degrading consortia (one methanogenic and one nitrate-reducing) on a physiological and molecular level. The shortest doubling times, 8 to 9 days, were observed in nitrate-reducing cultures. The highest substrate concentration utilized, 1000 muM, and maximum absolute rates of benzene degraded, 75 muM/day, were observed in methanogenic cultures. Five Bacterial 16S rRNA sequences, one of which resembled a clone previously found in a sulphate-reducing benzene-degrading culture, were identified in the methanogenic culture. Four Bacterial and no Archaeal 16S rRNA sequences were identified in the nitrate-reducing culture. One clone comprised 70% of the culture and was phylogenetically 93% similar to both Azoarcus and Dechloromonas species. The third objective was to isolate and characterize pure cultures capable of anaerobic benzene biodegradation. Two co-cultures called Dechloromonas co-culture (DCC) and Azoarcus co-culture (ACC) were successfully isolated from a nitrate-reducing enrichment culture. DCC is sim;99% Dechloromonas sp. and sim;1% an unidentified eubacterium clone. ACC is sim;98% Azoarcus sp. and sim;2% Pseudomonas sp. Both co-cultures were capable of anaerobic benzene, toluene and benzoate degradation under nitrate-reducing conditions. The isolated Pseudomonas sp. was capable of aerobic benzene degradation and hydrogen utilization under nitrate-reducing conditions. The isolated unidentified eubacterium clone did not exhibit growth on any of the substrates tested. The Dechloromonas and Azoarcus organisms are responsible for anaerobic benzene degradation. The fourth objective was to identify the key metabolic steps in the anaerobic benzene degradation pathways. 13C6-benzene experiments were conducted with the methanogenic and nitrate-reducing enrichments. Under methanogenic conditions a maximum of 8 muM 13C6-phenol and 3 muM 13C6-benzoate were detected. These results indicate that under methanogenic conditions a pathway where benzene undergoes hydroxylation to phenol and further transformation to benzoate exists. Under nitratereducing conditions a maximum of 90 nM 13C6-toluene, 120 nM 13C6-benzoate and no phenol were detected as intermediates of benzene degradation. This is the first evidence for a pathway where benzene undergoes methylation to toluene and further transformation to benzoate.
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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) | 0.001 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 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".