Structural investigation by tandem mass spectrometry analysis of a heterogeneous mixture of Lipid A <sub>n</sub> isolated from the lipopolysaccharide of <i>Aeromonas hydrophila</i> SJ‐55Ra
Bibliographic record
Abstract
Rationale We report herein the electrospray ionization mass spectrometry (ESI‐MS) negative ion mode and low‐energy collision‐induced dissociation tandem mass spectrometry (CID‐MS/MS) analysis of a mixture of lipid A n isolated from the lipopolysaccharide (LPS) of a rough‐resistant wild strain of the Gram‐negative bacteria Aeromonas hydrophila grown in the presence of phages (SJ‐55Ra). This investigation indicates that the presence of a mixture of lipid A acylated disaccharides, whose molecular structures were not relatively conserved, resulted from the incomplete LPS biosynthesis caused by the phage treatment. Methods The heterogeneous lipid A n mixture from the LPS‐SJ55Ra was obtained following growth of the Gram‐negative bacteria Aeromonas hydrophila (SJ‐55R) in the presence of phages and isolation by the aqueous phenol method. Following hydrolysis and purification of the lipopolysaccharide, ESI‐MS and low‐energy CID‐MS/MS analyses were performed on a triple‐quadrupole (QqQ) and a Fourier transform ion cyclotron resonance (FTICR) instrument. Results ESI‐MS analysis suggested that this lipid A n mixture contained eight molecular disaccharide anions and three monosaccharide anions. This series of lipid A n was asymmetrically substituted with ((R)‐14:0(3‐OH)) fatty acids located at O‐3 and N‐2 and with branched fatty acids: (Cl4:0(3‐(R)‐ O ‐C14:0)) and (C12:0(3‐(R)‐ O ‐(14:0)) at the O‐3′ and N‐2′ positions. Conclusions Tandem mass spectrometric analyses allowed the exact determination of the fatty acid acylation locations on the D‐Glc p N disaccharide. The MS/MS results established that it was possible to selectively cleave C–O, C–N, and C–C bonds, together with glycosidic C–O and cross‐ring cleavages, affording excellent structural analysis of lipid A biomolecules.
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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 | 0.000 | 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".