Identification of a Hydroxyproline Transport System in the Legume Endosymbiont <i>Sinorhizobium meliloti</i>
Bibliographic record
Abstract
Hydroxyproline-rich proteins in plants offer a source of carbon and nitrogen to soil-dwelling microorganisms in the form of root exudates and decaying organic matter. This report describes an ABC-type transport system dedicated to the uptake of hydroxyproline in the legume endosymbiont Sinorhizobium meliloti. We have designated genes involved in hydroxyproline metabolism as hyp genes and show that an S. meliloti strain lacking putative transport genes (DeltahypMNPQ) is unable to grow with or transport trans-4-hydroxy-l-proline when this compound is available as a sole source of carbon. Expression of hypM is upregulated in the presence of trans-4-hydroxy-l-proline and cis-4-hydroxy-d-proline, as modulated by a repressor (HypR) of the GntR/FadR subfamily. Although alfalfa root nodules contain hydroxyproline-rich proteins, we demonstrate that the transport system is not highly expressed in nodules, suggesting that bacteroids are not exposed to high levels of free hydroxyproline in planta. In addition to hypMNPQ, we report that S. meliloti encodes a second independent mechanism that enables transport of trans-4-hydroxy-l-proline. This secondary transport mechanism is induced in proline-grown cells and likely entails a system involved in l-proline uptake. This study represents the first genetic description of a prokaryotic hydroxyproline transport system, and the ability to metabolize hydroxyproline may contribute significantly toward the ecological success of plant-associated bacteria such as the rhizobia.
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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".