Salt tolerance of archaeal extremely halophilic lipid membranes: J.Biol.Chem.
Bibliographic record
Abstract
The membranes of extremely halophilic archaea are characterized by abundance of a diacidic phospholipid, archaetidylglycerol methylphosphate (PGP-Me), which accounts for 50-80 mol% of the polar lipids, and by the absence of phospholipids with choline, ethanolamine, inositol and serine head groups. These membranes are stable in concentrated 3-5M NaCl solutions, while membranes of non-halophilic archaea, which do not contain PGP-Me, are unstable and leaky in such conditions. By means of X-ray diffraction and vesicle permeability measurements we demonstrate that PGP-Me contributes in an essential way to membrane stability in hypersaline environments. Large unilamellar vesicles (LUV) prepared from the polar lipids of extreme halophiles, H. halobium and H. salinarum, retain entrapped carboxyfluorescein and resist aggregation in the whole range 0-4M NaCl, similarly to LUV prepared from purified PGP-Me. By contrast, LUV made of polar lipid extracts from moderately halophilic and non-halophilic archaea (M. jannaschii, M. mazei, M. smithii) are leaky and aggregate at high salt concentrations. However, adding PGP-Me to M. mazei lipids results in gradual enhancement of the LUV stability, in correlation with the PGP-Me content. The LUV data are substantiated by the X-ray results, which show that H. halobium and M. mazei lipids have dissimilar phase behavior and form different structures at high NaCl concentrations. H. halobium lipids maintain an expanded lamellar structure with spacing of 8.5-9 nm, which is stable up to at least 100 degrees C in 2M NaCl and up to ~60 degrees C in 4M NaCl, while M. mazei lipids form non-lamellar structures, represented by the Pn3m cubic phase and the inverted hexagonal HII phase. From these data, the forces preventing membrane aggregation in halophilic archaea appear to be steric repulsion due to the large head group of PGP-Me or, possibly, out-of-plane bilayer undulations rather than electrostatic repulsion due to the doubly charged PGP-Me head group
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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) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.001 |
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".