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Bacterial mesosomes: method dependent artifacts
Abstract:
The occurrence of mesosomes was investigated during septum formation of vegetative and sporulating cells of Bacillus cereus. It has been demonstrated that bacterial mesosomes which are considered by numerous microbiologists as an integrated constituent of Gram positive bacteria, are in reality artifacts arising during the preparation for electron microscopy. The conventional fixation methods allowed enough time for the cytoplasmic membrane to react to the changed conditions and to form the typical pocket-like membrane invaginations. With cryofixation followed by freeze-substitution it was shown in ultrathin sections that mesosomes do not occur. The extremely rapid freezing and the substitution of the ice by an organic solvent containing the fixative prevented the formation of membraneous artifacts.
Insights
Bacterial mesosomes, once thought to be real cell structures, are actually artifacts. Advanced cryofixation techniques reveal these membrane structures do not exist in Bacillus cereus.
Area of Science:
- Microbiology
- Cell Biology
- Microscopy Techniques
Background:
- Mesosomes were historically considered integral components of Gram-positive bacteria.
- Their role in cellular processes like septum formation was widely accepted.
Purpose of the Study:
- To investigate the true occurrence of mesosomes during Bacillus cereus cell division.
- To determine if mesosomes are genuine cellular structures or preparation artifacts.
Main Methods:
- Investigated mesosome formation during vegetative and sporulating cell division in Bacillus cereus.
- Compared conventional fixation methods with rapid cryofixation followed by freeze-substitution for electron microscopy.
Main Results:
- Conventional fixation methods led to the formation of artifactual, pocket-like membrane invaginations, identified as mesosomes.
- Cryofixation and freeze-substitution demonstrated the absence of mesosomes in ultrathin sections.
- Rapid freezing prevented the formation of these membraneous artifacts.
Conclusions:
- Mesosomes are not real constituents of Bacillus cereus cells.
- They are artifacts generated during sample preparation for electron microscopy, particularly with conventional fixation techniques.