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 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 | 0.001 | 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 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".