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Effects of mot gene expression on the structure of the flagellar motor
1Department of Anatomy, Albert Einstein College of Medicine, Bronx, NY 10461.
Abstract:
Direct freezing procedures have enabled us to visualize distinctive intramembrane particle ring structures in the cytoplasmic membranes of peritrichously flagellated bacteria by means of freeze-fracture electron microscopy. These structures were identified as flagellar motor components because their distribution matched that of flagella, and because they were absent in non-flagellated mutants of Escherichia coli. Particle rings were present in both the Gram-positive Streptococcus and the Gram-negative E. coli. In E. coli, a non-functional mocha operon produced flagellated but immotile cells lacking the particle rings. Simultaneous introduction of the motA and motB genes, led to recovery of both motility and the ring structures but neither gene alone was sufficient. The concomitant loss of the rings and motility is consistent with the ring particles having a central role in the flagellar motor.
Insights
Distinctive ring structures in bacterial membranes are identified as crucial flagellar motor components. Their presence and function are linked to bacterial motility, particularly in Escherichia coli.
Area of Science:
- Microbiology
- Cell Biology
- Biophysics
Background:
- Bacterial flagella are complex rotary machines responsible for motility.
- The precise structure and function of flagellar motor components remain incompletely understood.
- Intramembrane particle arrangements in bacterial membranes are often associated with functional structures.
Purpose of the Study:
- To visualize and identify intramembrane particle structures associated with bacterial flagellar motors.
- To determine the role of these structures in bacterial motility.
- To investigate the genetic basis of these structures in Escherichia coli.
Main Methods:
- Freeze-fracture electron microscopy was employed to visualize bacterial membrane structures.
- Comparative analysis was performed between flagellated and non-flagellated bacterial mutants.
- Genetic manipulation of the mocha operon and motA/motB genes in Escherichia coli was conducted.
Main Results:
- Distinctive intramembrane particle ring structures were visualized in the cytoplasmic membranes of flagellated bacteria.
- These particle rings were absent in non-flagellated mutants of Escherichia coli.
- Motility and particle rings were restored in immotile E. coli mutants only upon simultaneous introduction of motA and motB genes.
Conclusions:
- The visualized particle rings represent key components of the bacterial flagellar motor.
- The motA and motB genes are essential for the formation of these motor structures and subsequent motility.
- These findings provide direct evidence for the role of these ring structures in enabling bacterial flagellar function.