Comparative genomic analysis of <i>Bradyrhizobium</i> strains with natural variability in the efficiency of nitrogen fixation, competitiveness, and adaptation to stressful edaphoclimatic conditions
Bibliographic record
Abstract
ABSTRACT Bradyrhizobium is known for its ability to fix atmospheric nitrogen in symbiosis with agronomically important crops. This study focused on two groups of strains, each containing eight putative natural variants of B. japonicum SEMIA 586 (=CNPSo 17) or B. diazoefficiens SEMIA 566 (=CNPSo 10), previously used as commercial inoculants for soybean crops in Brazil. We aimed to detect genetic variations that might be related to biological nitrogen fixation, competitiveness for nodule occupancy, and adaptation to the stressful conditions of the Brazilian Cerrado soils. High-quality genome assemblies were produced for all strains and used for comparative genomic analyses. The core genome phylogeny revealed that strains of each group are closely related, confirmed by high average nucleotide identity (ANI) values. However, variants accumulated divergences resulting from horizontal gene transfer (HGT), genomic rearrangements, and nucleotide polymorphisms. The B. japonicum group presented a larger pangenome and a higher number of nucleotide polymorphisms than the B. diazoefficiens group, probably due to its longer adaptation time to the Cerrado soil. Interestingly, five strains of the B. japonicum group carry two plasmids. The genetic variability found in both groups is discussed in light of the observed differences in their nitrogen fixation capacity, competitiveness for nodule occupancy, and environmental adaptation. SIGNIFICANCE The two main reference strains for soybean inoculation in Brazil, B. japonicum CPAC 15 (=SEMIA 5079) and B. diazoefficiens CPAC 7 (=SEMIA 5080), have been considered highly competitive and highly efficient in nitrogen fixation, respectively. In this study, we obtained and analyzed the genomes of the parental and variant strains. We detected two plasmids in five strains and several genetic differences that might be related to adaptation to the stressful conditions of the soils of the Brazilian Cerrado biome. We also detected genetic variations in specific regions that may impact symbiotic nitrogen fixation. Our analysis contributes to new insights into evolution of Bradyrhizobium , and some of the identified differences may be applied as genetic markers to assist strain selection programs.
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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 | 0.001 | 0.001 |
| 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".