Intragenomic Heterogeneity and Intergenomic Recombination among Haloarchaeal rRNA Genes
Bibliographic record
Abstract
More than one copy of rRNA operons, which code for both the small-subunit (SSU) and large-subunit (LSU) rRNA, are often found in prokaryotes. It is generally assumed that all rRNA operons within a single cell are almost identical. A notable exception is the extremely halophilic archaeal genus Haloarcula, most species of which are known to harbor highly divergent rRNA operons that differ at approximately 5% of the nucleotide positions in the SSU gene and at 1 to 2% of the nucleotide positions in the LSU gene. We report that such intragenomic heterogeneity is not unique to Haloarcula, as high levels of intragenomic sequence variation have been observed for the SSU genes of two other genera of extreme halophiles, Halosimplex and Natrinema. To investigate this in detail, the two rRNA operons of Halosimplex carlsbadense and the four operons of Natrinema sp. strain XA3-1 were cloned and completely sequenced. The SSU and LSU genes of H. carlsbadense show the highest levels of intragenomic heterogeneity observed so far in archaea (6.7 and 2.6%). The operons of Natrinema sp. strain XA3-1 have additional unusual characteristics, such as identical internal transcribed spacers, while one of four SSU genes is 5% divergent and all LSU genes differ from each other by 0.9 to 1.9%. The heterogeneity among the Natrinema sp. strain XA3-1 LSU genes is localized in hot spots, and one of these regions is shown to be the result of a recombination event with a distantly related halophile. This is the first example of interspecies recombination between rRNA genes in archaea, and the recombination occurred over one of the largest phylogenetic distances ever reported for such an event. We suggest that intragenomic heterogeneity of rRNA operons is an ancient and stable trait in several lineages of the Halobacteriales. The impact of this phenomenon on the taxonomy of extremely halophilic archaea is discussed.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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 teacher head, 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".