Deconstructing the redox cascade: what role do microbial exudates (flavins) play?
Bibliographic record
Abstract
Environmental contextRedox potential is a controlling variable in aquatic chemistry. Through time series data, we show that microbial exudates released by bacteria may control trends in redox potential observed in natural waters. In particular, electron transfer between these exudates and the electrode could explain the values measured in the presence of abundant oxidants such as oxygen and nitrate. AbstractRedox electrodes are commonly used to measure redox potentials (EH) of natural waters. The recorded EH values are usually interpreted in terms of the dominant inorganic redox couples. To further advance the interpretation of measured EH distributions along temporal and spatial redox gradients, we performed a series of reactor experiments in which oxidising and reducing conditions were alternated by switching between sparging with air and N2. Starting from a simple electrolyte solution and ending with a complex biogeochemical system, common groundwater solutes, metabolic substrates (NO3− and C3H5O3−), bacteria (Shewanella oneidensis MR-1) and goethite (α-FeOOH(s)) were tested by increasing the system complexity with each subsequent experiment. This systematic approach yielded a redox cascade ranging from +500 to −350 mV (pH ~7.4). The highest and lowest EH values registered by the platinum (Pt) electrode agreed with Nernstian redox potentials predicted for the O2/H2O2 and FeOOH/Fe2+(aq) couples respectively. Electrode poisoning by the organic pH buffer (MOPS) and addition of bacteria to the aerated solutions resulted in marked decreases in measured EH values. The latter effect is attributed to the release of flavins by Shewanella oneidensis MR-1 to the medium. As expected, equilibrium with the non-electroactive NO3−/NO2−/NH4+ redox couples could not account for the EH values recorded during dissimilatory nitrate reduction to ammonium (DNRA). However, the observed EH range for DNRA coincided with that bracketed by EH values measured in separate abiotic solutions containing either the oxidised (+324 ± 29 mV) or reduced (−229 ± 40 mV) forms of flavins. The results therefore suggest that the Pt electrode detected the presence of the electroactive flavins, even at submicromolar concentrations. In particular, flavins help explain the fairly low EH values measured in the presence of strong oxidants, such as O2 and NO3−.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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 | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.009 | 0.001 |
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; both teacher heads agree on what is shown here.
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".