Distinct Acetate Utilization Strategies Differentiate Butyrate and Medium-Chain Carboxylic Acid Producing Chain-Elongating Bacteria
Bibliographic record
Abstract
Abstract Chain elongating bacteria (CEB) are a unique guild of anaerobes that upcycle organic waste into valuable short- and medium-chain carboxylic acids (MCCAs), enabling a circular bioeconomy. However, the metabolic rules that determine product chain length have remained elusive. Here, we combine 13 C isotope tracing, proteomics, enzyme assays, and metabolic modelling to show that distinct acetate utilization strategies underlie the divergence between butyrate- and MCCA-producing CEB. MCCA-producing strains recycle acetate to maximize lactate use under acetate limitation, but at the cost of slower growth. In contrast, butyrate-producing strains grow faster by favoring acetate assimilation, at the cost of restricted lactate utilization when acetate is scarce. These physiological trade-offs are encoded in the substrate specificity of coenzyme A transferase, the terminal enzyme in reverse β-oxidation. Our findings uncover a fundamental constraint shaping chain-length selectivity in CEB and offer new strategies to optimize MCCA production from organic waste streams.
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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) | 0.001 | 0.001 |
| 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 | 0.001 | 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 teacher head, 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".