Stable Carbon Isotope Ratios of Lipid Biomarkers of Sulfate-Reducing Bacteria
Bibliographic record
Abstract
We examined the potential use of natural-abundance stable carbon isotope ratios of lipids for determining substrate usage by sulfate-reducing bacteria (SRB). Four SRB were grown under autotrophic, mixotrophic, or heterotrophic growth conditions, and the delta13C values of their individual fatty acids (FA) were determined. The FA were usually 13C depleted in relation to biomass, with Deltadelta13C(FA - biomass) of -4 to -17 per thousand; the greatest depletion occurred during heterotrophic growth. The exception was Desulfotomaculum acetoxidans, for which substrate limitation resulted in biomass and FA becoming isotopically heavier than the acetate substrate. The delta13C values of FA in Desulfotomaculum acetoxidans varied with the position of the double bond in the monounsaturated C16 and C18 FA, with FA becoming progressively more 13C depleted as the double bond approached the methyl end. Mixotrophic growth of Desulfovibrio desulfuricans resulted in little depletion of the i17:1 biomarker relative to biomass or acetate, whereas growth with lactate resulted in a higher proportion of i17:1 with a greater depletion in 13C. The relative abundances of 10Me16:0 in Desulfobacter hydrogenophilus and Desulfobacterium autotrophicum were not affected by growth conditions, yet the Deltadelta13C(FA - substrate) values of 10Me16:0 were considerably greater during autotrophic growth. These experiments indicate that FA delta13C values can be useful for interpreting carbon utilization by SRB in natural environments.
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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 | 0.000 | 0.001 |
| 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 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".