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Studies of sigma D-dependent functions in Bacillus subtilis
L M Márquez1, J D Helmann, E Ferrari
1Department of Biochemistry, University of California, Berkeley 94720.
Journal of Bacteriology
|June 1, 1990
Summary
Sigma D (sigma 28) in Bacillus subtilis is crucial for flagellar synthesis and chemotaxis. Its absence or reduction impairs flagellin production, cell separation, and motility, highlighting its regulatory role.
Area of Science:
- Microbiology
- Molecular Biology
- Bacterial Genetics
Background:
- Gene expression in Bacillus subtilis is regulated by sigma factors controlling RNA polymerase activity.
- Sigma D (sigma 28) is a sigma factor involved in transcribing genes during vegetative growth and early stationary phases.
- Previous studies linked sigma D to flagellar synthesis and chemotaxis.
Purpose of the Study:
- To investigate the functions of sigma D (sigD) in Bacillus subtilis, particularly concerning flagellar synthesis and chemotaxis.
- To analyze the effects of reduced or absent sigma D levels on bacterial growth, motility, and cell division.
Main Methods:
- Studied B. subtilis strains with disrupted or reduced levels of the sigma D structural gene (sigD).
- Analyzed flagellin synthesis, cell morphology, methyl-accepting chemotaxis protein production, and autolysin activities.
- Utilized genetic insertions upstream and downstream of the sigD gene to assess gene regulation and function.
- Performed genetic experiments to determine allelism with the flaB locus.
Main Results:
- A null mutant lacking sigma D failed to synthesize flagellin, grew as long filaments, lacked methyl-accepting chemotaxis proteins, and showed reduced autolysin activity.
- A strain with reduced sigma D levels exhibited impaired chemotaxis/motility and grew in short chains.
- Insertions downstream of sigD also resulted in impaired chemotaxis/motility, suggesting involvement of downstream genes.
- The sigD gene was found to be allelic to the flaB locus, affecting flagellin expression.
Conclusions:
- Sigma D is essential for flagellin synthesis, proper cell separation, and chemotaxis in B. subtilis.
- Reduced sigma D levels significantly impact bacterial motility and cell division.
- The sigD gene may be part of an operon, and downstream genes also play roles in chemotaxis and motility.
- Sigma D's role extends beyond flagellar synthesis to encompass broader cellular functions.