Regulation of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) metabolism in Shewanella halifaxensis HAW-EB4 by terminal electron acceptor and involvement of c-type cytochrome
Bibliographic record
Abstract
Shewanella halifaxensis HAW-EB4 was previously isolated for its potential to mineralize hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) from a UXO (unexploded ordnance)-contaminated marine sediment site near Halifax Harbor. The present study was undertaken to determine the effect of terminal electron acceptors (TEA) on the growth of strain HAW-EB4 and on the enzymic processes involved in RDX metabolism. The results showed that aerobic conditions were optimal for bacterial growth, but that anaerobic conditions in the presence of trimethylamine N-oxide (TMAO) or in the absence of TEA favoured RDX metabolism. RDX as a substrate neither stimulated respiratory growth nor induced its own biotransformation. Strain HAW-EB4 used periplasmic proteins to transform RDX to both nitroso [hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine (MNX), hexahydro-1,3-dinitroso-5-nitro-1,3,5-triazine (DNX), and hexahydro-1,3,5-trinitroso-1,3,5-triazine (TNX)] and ring cleavage products (such as methylenedinitramine), with more nitroso formation in cells grown on TMAO or pre-incubated in the absence of TEA. Using spectroscopy, SDS-PAGE and haem-staining analysis, strain HAW-EB4 was found to produce different sets of c-type cytochromes when grown on various TEA, with several more cytochromes produced in cells grown on TMAO. Crude cytochromes from total periplasmic proteins of TMAO-grown cells metabolized RDX to products similar to those found in assays using total periplasmic proteins and whole cells. To prove the involvement of cytochrome in RDX metabolism, we monitored dithionite- or NADH-reduced cytochromes by their absorbance at the alpha (551 nm) or gamma (418-420 nm) bands during anaerobic incubation with RDX. In both cases we found that RDX biotransformation was accompanied by oxidation of reduced cytochrome. Furthermore, O(2), an oxidant of reduced cytochrome, inhibited RDX transformation. The present results demonstrate that S. halifaxensis HAW-EB4 metabolizes RDX optimally under TMAO-reducing conditions, and that c-type cytochromes are involved.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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) | 0.001 | 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".