<i>Azoarcus</i> Grass Endophytes Contribute Fixed Nitrogen to the Plant in an Unculturable State
Bibliographic record
Abstract
The extent to which the N2-fixing bacterial endophyte Azoarcus sp. strain BH72 in the rhizosphere of Kallar grass can provide fixed nitrogen to the plant was assessed by evaluating inoculated plants grown in the greenhouse and uninoculated plants taken from the natural environment. The inoculum consisted of either wild-type bacteria or nifK- mutant strain BHNKD4. In N2-deficient conditions, plants inoculated with strain BH72 (N2-fixing test plants) grew better and accumulated more nitrogen with a lower delta15N signature after 8 months than did plants inoculated with the mutant strain (non-N2-fixing control plants). Polyadenylated or polymerase chain reaction-amplified BH72 nifH transcripts were retrieved from test but not from control plants. BH72 nifH transcripts were abundant. The inocula could not be reisolated. These results indicate that Azoarcus sp. BH72 can contribute combined N2 to the plant in an unculturable state. Abundant BH72 nifH transcripts were detected also in uninoculated plants taken from the natural environment, from which Azoarcus sp. BH72 also could not be isolated. Quantification of nitrogenase gene transcription indicated a high potential of strain BH72 for biological N2 fixation in association with roots. Phylogenetic analysis of nitrogenase sequences predicted that uncultured grass endophytes including Azoarcus spp. are ecologically dominant and play an important role in N2-fixation in natural grass ecosystems.
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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".