An overview of the occurrence of ether- and ester-linked iso-diabolic acid membrane lipids in microbial cultures of the Acidobacteria: Implications for brGDGT paleoproxies for temperature and pH
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Bibliographic record
Abstract
13,16-Dimethyl octacosanedioic acid (<i>iso</i>-diabolic acid) is a major membrane-spanning lipid of subdivisions (SDs) 1, 3 and 4 of the Acidobacteria, a highly diverse phylum within the Bacteria. It has been suggested that these lipids are potential building blocks for the orphan bacterial glycerol dialkyl glycerol tetraethers (GDGT) that occur widely in a variety of environmental settings. Here, we expand the knowledge on the occurrence of <i>iso</i>-diabolic acid in Acidobacteria by examining the lipid composition of six strains belonging to SDs 6, 8, 10, and 23 of the Acidobacteria, not previously analyzed for these lipids. In addition, we examined 12 new strains belonging to SDs 1, 3 and 4. Acid hydrolysis of total cell material released <i>iso</i>-diabolic acid in substantial quantities (25–39% of all fatty acids) from the strains of SDs 1 and 3 (except “<i>Candidatus</i> Solibacter usitatus), and, for the first time, strains of SD 6 (6–25%), but not from SDs 8, 10, and 23. The monoglycerol ether derivative of <i>iso</i>-diabolic acid was only dominantly present in SD 4 strains (17–34%), indicating that the occurrence of ether-bound <i>iso</i>-diabolic acid is mainly restricted to SD 4 species. Methylated <i>iso</i>-diabolic acid derivatives were encountered in SDs 1, 3, 4, and 6, but only SD 4 species produced 5-methyl <i>iso</i>-diabolic acid derivatives, whereas the other SDs formed 6-methyl <i>iso</i>-diabolic acids. This suggests that the position of methylation of <i>iso</i>-diabolic acid may be controlled by the phylogenetic affiliation within the Acidobacteria and thus may not be a direct but an indirect response environmental to environmental conditions as inferred from the bacterial GDGT distributions in soil, peat and rivers
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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 | 0.000 |
| 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 it