Osmoadaptative Strategy and Its Molecular Signature in Obligately Halophilic Heterotrophic Protists
Bibliographic record
Abstract
Halophilic microbes living in hypersaline environments must counteract the detrimental effects of low water activity and salt interference. Some halophilic prokaryotes equilibrate their intracellular osmotic strength with the extracellular milieu by importing inorganic solutes, mainly potassium. These "salt-in" organisms characteristically have proteins that are highly enriched with acidic and hydrophilic residues. In contrast, "salt-out" halophiles accumulate large amounts of organic solutes like amino acids, sugars and polyols, and lack a strong signature of halophilicity in the amino acid composition of cytoplasmic proteins. Studies to date have examined halophilic prokaryotes, yeasts, or algae, thus virtually nothing is known about the molecular adaptations of the other eukaryotic microbes, that is, heterotrophic protists (protozoa), that also thrive in hypersaline habitats. We conducted transcriptomic investigations to unravel the molecular adaptations of two obligately halophilic protists, Halocafeteria seosinensis and Pharyngomonas kirbyi Their predicted cytoplasmic proteomes showed increased hydrophilicity compared with marine protists. Furthermore, analysis of reconstructed ancestral sequences suggested that, relative to mesophiles, proteins in halophilic protists have undergone fewer substitutions from hydrophilic to hydrophobic residues since divergence from their closest relatives. These results suggest that these halophilic protists have a higher intracellular salt content than marine protists. However, absence of the acidic signature of salt-in microbes suggests that Haloc. seosinensis and P. kirbyi utilize organic osmolytes to maintain osmotic equilibrium. We detected increased expression of enzymes involved in synthesis and transport of organic osmolytes, namely hydroxyectoine and myo-inositol, at maximal salt concentration for growth in Haloc. seosinensis, suggesting possible candidates for these inferred organic osmolytes.
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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".