Production of the cobalamin lower ligand, 5,6-dimethylbenzimidazole, by a diatom under cobalamin-deplete conditions
Bibliographic record
Abstract
Abstract Cobalamin, or vitamin B 12 , is a micronutrient required by half of all surveyed phytoplankton but produced only by select bacteria and archaea. Cobalamin influences community composition and primary productivity in various regions of the ocean and has been shown to be a critical currency in microbial interactions. Many marine microorganisms can salvage cobinamide and remodel pseudocobalamin, to generate cobalamin using the lower ligand 5,6-dimethylbenzimidazole (DMB), or the ribosylated form, α-ribazole. The sources of the cobalamin lower ligand and intermediate remain poorly characterized but are currently attributed to prokaryotes alone. Here, we grew axenic cultures of a recently isolated Thalassiosiraceae diatom over a range of cobalamin concentrations (0, 0.75, 10, 100 pM). Then, using mass spectrometry, we quantified cobalamin and α-ribazole in both particulate (cellular) and dissolved (media) phases. We found that this diatom is a facultative cobalamin consumer: it takes up cobalamin when available but can survive in its absence. Strikingly, under low cobalamin availability, we demonstrate that the diatom produces α-ribazole. This highlights eukaryotic production as a source of the molecule and suggests that salvaging and remodeling by phytoplankton may be less dependent on prokaryotes than previously imagined. We detected α-ribazole in the spent media during stationary phase, highlighting eukaryotic production of the molecule as a public good. We provide evidence that α-ribazole is produced by this diatom as a mechanism to cope with low cobalamin availability, suggesting that even amongst organisms that don’t absolutely require it, cobalamin use has important consequences for fitness. Importance Section Cobalamin (vitamin B 12 ) is a scarce micronutrient in the ocean that impacts the composition and activity of marine microbial communities. Microbes employ a range of strategies to cope with low cobalamin availability, including remodeling cobalamin intermediates and alternatives into cobalamin when the lower ligand is available. Here we show that a recently isolated Thalassiosiraceae diatom doesn’t need cobalamin to survive but will take it up and use it when available. Additionally, the diatom produces the lower ligand (α-ribazole) under low cobalamin conditions. The production of α-ribazole was previously thought to be restricted to bacteria and archaea, so these results suggest that eukaryotes could play a larger role in cobamide remodeling than previously imagined. This work also demonstrates that even organisms that don’t absolutely require cobalamin for survival have adopted metabolic strategies to cope with its absence, emphasizing the importance of this vitamin for phytoplankton metabolism.
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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) | 0.000 | 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 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".