SIDEROPHORE-INDEPENDENT IRON UPTAKE BY IRON-LIMITED CELLS OF THE CYANOBACTERIUM ANABAENA FLOS-AQUAE1
Bibliographic record
Abstract
Iron acquisition by iron-limited cyanobacteria is typically considered to be mediated mainly by siderophores, iron-chelating molecules released by iron-limited cyanobacteria into the environment. In this set of experiments, iron uptake by iron-limited cells of the cyanobacterium Anabaena flos-aquae (L.) Bory was investigated in cells resuspended in siderophore-free medium. Removal of siderophores decreased iron-uptake rates by ∼60% compared to siderophore-replete conditions; however, substantial rates of iron uptake remained. In the absence of siderophores, Fe(III) uptake was much more rapid from a weaker synthetic chelator [N-(2-hydroxyethyl)ethylenediamine-N,N′,N′-triacetic acid (HEDTA); log Kcond = 28.64 for Fe(III)HEDTA(OH)−] than from a very strong chelator [N,N′-bis(2-hydroxybenzyl)-ethylenediamine-N,N′-diacetic acid (HBED); log Kcond = 31.40 for Fe(III)HBED−], and increasing chelator:Fe(III) ratios decreased the Fe(III)-uptake rate; these results were evident in both short-term (4 h; absence of siderophores) and long-term (116 h; presence of siderophores) experiments. However, free (nonchelated) Fe(III) provided the most rapid iron uptake in siderophore-free conditions. The results of the short-term experiments are consistent with an Fe(III)-binding/uptake mechanism associated with the cyanobacterial outer membrane that operates independently of extracellular siderophores. Iron uptake was inhibited by temperature-shock treatments of the cells and by metabolically compromising the cells with diphenyleneiodonium; this finding indicates that the process is dependent on active metabolism to operate and is not simply a passive Fe(III)-binding mechanism. Overall, these results point to an important, siderophore-independent iron-acquisition mechanism by iron-limited cyanobacterial cells.
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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 | 0.000 | 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".