Biosynthesis of polyketides produced by marine microbes
Bibliographic record
Abstract
The most widely studied of all secondary metabolites, the polyketides (PKs), are low molecular weight compounds assembled via sequential condensations of small carboxylic acids. Biosynthetic and molecular genetic knowledge pertaining to PK production, mostly from studies of terrestrial microbes, have revealed the primary role of polyketide synthase (PKS) enzymes, which condense carboxylic acids to form highly functionalized metabolites. Studies on the biosynthesis of PKs produced by marine species revealed more complex pathways than those encountered in terrestrial species. In this study, we isolated PKS gene fragments from marine isolates of filamentous fungi via degenerate PCR. Phylogenetic comparison with corresponding sequences from terrestrial-derived fungi revealed a dichotomy, (consistent with a previous study involving terrestrial fungi only), between PKSs producing non-reduced (NR) PKs and those producing partially reduced (PR) PKs, but no clear division between sequences from marine and terrestrial fungi. PCR amplification of a PR-type gene fragment from a marine isolate of Apiospora montagnei is consistent with the production of an aromatic compound, papulacandin B (PapB) by this species. We have established that PapB is assembled via a PK pathway by way of experiments involving stable isotope precursor incorporation in conjunction with 13C NMR spectroscopy. We extended the investigation to the biosynthesis of PKs of marine dinoflagellates. Although attempts to isolate PKS genes from dinoflagellate DNA or a constructed cDNA library were unsuccessful, stable isotope incorporation studies of DTX-5, a putative PK produced by the dinoflagellate Prorocentrum maculosum, (1) established the PK mechanism of its biosynthesis, (2) revealed a rare carbon deletion step and (3) demonstrated the incorporation of an intact amino acid into the structure. Mechanisms are proposed for the biosyntheses of PapB and DTX-5.
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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) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.006 | 0.005 |
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".