Free-living psychrophilic bacteria of the genus <i>Psychrobacter</i> are descendants of pathobionts
Bibliographic record
Abstract
Abstract Host-adapted microbiota are generally thought to have evolved from free-living ancestors. This process is in principle reversible, but examples are few. The genus Psychrobacter (family Moraxellaceae , phylum Gamma-Proteobacteria ) includes species inhabiting diverse and mostly polar environments, such as sea ice and marine animals. To probe Psychrobacter’s evolutionary history, we analyzed 85 Psychrobacter strains by comparative genomics and phenotyping under 24 different growth conditions. Genome-based phylogeny shows Psychrobacter are derived from Moraxella , which are warm-adapted pathobionts. Psychrobacter strains form two ecotypes based on growth temperature: flexible (FE, growth at 4 - 37°C), and restricted (RE, 4 - 25°C). FE strains, which can be either phylogenetically basal or derived, have smaller genomes and higher transposon copy numbers. RE strains have larger genomes, and show genomic adaptations towards a psychrophilic lifestyle and are phylogenetically derived only. We then assessed Psychrobacter abundance in 86 mostly wild polar bear stools and tested persistence of select strains in germfree mice. Psychrobacter (both FE and RE) was enriched in stool of polar bears feeding on mammals, but only FE strains persisted in germfree mice. Together these results indicate growth at 37°C is ancestral in Psychrobacter , lost in many derived species, and likely necessary to colonize the mammalian gut.
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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 | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".