Influence of carbon-to-nitrogen ratio on the denitrifying activities of a methanol-fed, marine recirculating denitrification reactor, and the evolution of the bacteria community during the operating process
Bibliographic record
Abstract
Abstract Background Carbon-to-nitrogen ratio (C/N) is an essential parameter known to influence both the function and the activity of microbial communities in bioprocesses. The right balance between the contribution of each of these resources are essential for sustainable and cost-efficiency bioprocess. Here we aimed to assess the influence of C/N (here methanol and nitrate) on the performance of a recirculating denitrifying reactor for 31 weeks under marine conditions. We also monitored the evolution of its microbial community during the operating conditions. Methodology A 500-mL methanol-fed recirculating denitrification reactor operated under marine conditions and colonized by a naturally occurring multispecies denitrifying biofilm was subjected to eight different C/N over 31 weeks under anoxic conditions. We monitored several physico-chemical parameters (denitrifying activities, methanol consumption, CO 2 production) throughout the operating conditions. Evolution of the bacterial community in the biofilm during the operating conditions was determined by 16S rRNA gene amplicon sequencing. Metatranscriptomes of representative conditions were performed to derive (1) the relative gene expression profiles of Methylophaga nitratireducenticrescens strain GP59, the main denitrifier, and (2) the functional diversity of the biofilm. Results Changes in C/N did not impact the denitrifying activities of the recirculating reactor but did impact the carbon dynamics. Throughout the operating time, nitrite and N 2 O appeared transiently, and ammonium was not observed. The bacterial community in the reactor increased in diversity as the biofilm aged, especially in heterotrophic bacteria, at the expense of methylotrophic bacteria. The functional diversity suggests that heterotrophs could use formaldehyde, which may have been released by methylotrophs in the biofilm, as energy and carbon source. The relative expression profiles of strain GP59 in the biofilm is distinct of those of GP59 planktonic pure cultures, and that the expression of several riboswitches and xoxF would be involved in such differences. Conclusions When the biofilm community is well established in the reactor, it can sustain changes in C/N with limited impact on the denitrification performance. Increase in the proportion of heterotrophs would allow the reactor to be more flexible for carbon sources. Such knowledge can be useful in the optimisation of denitrification process.
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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".