Abstract
Cells of Bacillus firmus OF4 and Bacillus alcalophilus were examined by rapid-freeze freeze-fracture and freeze-substitution electron microscopy. No special vesicular structures linked to growth at alkaline pH were found, either within or associated with the cytoplasmic membrane. The cytoplasmic membranes of the alkaliphilic bacilli and the neutrophilic Bacillus subtilis BD99 were indistinguishable. Distinctive intramembrane particle rings, presumed to be flagellar structures on the basis of distribution and morphological characteristics, were found in all of these species. These observations indicate that the adaptations required to effect oxidative phosphorylation and flagellar rotation at extreme alkaline pH occur without gross morphological rearrangement.
Highlights
The P-fracture face [11] of the lipid bilayer, in the two alkaliphilic Bacillus species, had a smooth surface studded with intramembrane particles (Fig. 1)
Immunolabeling had previously indicated a global distribution of the F1F0 ATP synthase in the membranes of the alkaliphilic bacilli
We found no hint of a corresponding global distribution of bulges or pits that might be indicative of enclosed membranous spaces of size sufficient to harbor assemblies of whole respiratory chains and the ATP synthase as proposed by others [1, 18]
Summary
Membrane Ultrastructure of Alkaliphilic Bacillus Species Studied by Rapid-Freeze Electron Microscopy No special vesicular structures linked to growth at alkaline pH were found, either within or associated with the cytoplasmic membrane. The cytoplasmic membranes of the alkaliphilic bacilli and the neutrophilic Bacillus subtilis BD99 were indistinguishable.
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