Outer‐membrane siderophore receptors of heterotrophic oceanic bacteria
Bibliographic record
Abstract
Pathogenic gram‐negative bacteria use specific receptors to transport ferric siderophore complexes across their outer membrane during iron (Fe)‐limited growth. Receptors such as these have not yet been characterized in oceanic heterotrophic bacteria. We examined four species of γ‐proteobacteria for the presence of Fe‐siderophore receptors with the use of a nondenaturing polyacrylamide gel electrophoresis binding assay and the siderophore ferrioxamine B (FB) labeled with 55Fe. Small‐subunit rRNA sequence analysis assigned these bacteria to the genera Pseudoalteromonas and Alteromonas. Two oceanic species, Pseudoalteromonas haloplanktis (Neptune) and Alteromonas macleodii (Jul88), which were shown previously to transport and assimilate Fe bound to FB during growth, synthesized an outer‐membrane FB receptor under Fe‐limiting conditions. Only low concentrations of the receptors were detected in these bacteria when they were grown with high concentrations of Fe. The FB receptor of P. haloplanktis (Neptune) had an apparent molecular mass of 79 kDa and an externally oriented binding site. The molecular mass of the receptor of A. macleodii (Jul88) was 100 kDa. No FB receptors were detected by our methods in two coastal species, Pseudoalteromonas rubra (LMG1) and Pseudoalteromonas piscicida (PWF3). P. haloplanktis (Neptune) and A. macleodii (Jul88) also bound 55Fe‐ferrichrome, a trihydroxamate siderophore like FB. Binding assays conducted with 115 nmol L−1 55Fe‐FB in the presence of increasing concentrations of desferrioxamine B showed a progressive decrease in the amount of 55Fe‐FB bound by the receptor protein, suggesting strong affinity of the receptor for the Fe‐free siderophore. Our results provide the first demonstration of Fe‐siderophore receptors in oceanic heterotrophic bacteria.
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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) | 0.001 | 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".