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Visualization of the subcellular location of sporulation proteins in Bacillus subtilis using immunofluorescence
K Pogliano1, E Harry, R Losick
1Department of Molecular and Cellular Biology, The Biological Laboratories, Harvard University, Cambridge, Massachusetts 02138, USA.
Abstract:
We describe the application of immunofluorescence microscopy to visualization of the subcellular localization of proteins involved in coat morphogenesis and chromosome packaging during the process of sporulation in Bacillus subtilis. In confirmation and extension of previous findings, we show that SpolVA, which is responsible for guiding coat formation to the surface of the outer membrane that surrounds the developing spore, assembles into a shell that is located close to or on the surface of this enveloping membrane. CotE, which is responsible for the formation of the outer layer of the coat, assembles into a second shell of apparently larger diameter. Assembly of SpolVA could be detected as early as the morphological stage of polar septation and closely followed the enveloping membrane of the mother cell during the stage of engulfment, thereby providing a sensitive and diagnostic marker for this phagocytic-like process. Surprisingly, the chromosome of the developing spore and the small, acid-soluble proteins, known as alpha/beta-type SASPs, that are known to coat the spore chromosome, were found to co-localize to a doughnut-like ring of approximately 1 micrometer in diameter. The use of a double mutant lacking the alpha/beta-type SASP demonstrated that these high abundance, DNA-binding proteins are responsible for packaging the chromosome of the developing spore into this unusual structure. We conclude that sporulation in B. subtilis is a fertile system for addressing cell biological problems in a bacterium and that immunofluorescence microscopy provides a sensitive method for visualizing protein subcellular localization at high resolution.
Insights
Immunofluorescence microscopy visualizes Bacillus subtilis sporulation. Small, acid-soluble proteins (SASPs) package the spore chromosome into a unique ring structure, revealing new insights into bacterial cell biology.
Area of Science:
- Bacterial cell biology
- Microbiology
- Molecular biology
Background:
- Sporulation in Bacillus subtilis is a complex developmental process.
- Understanding protein localization is crucial for elucidating sporulation mechanisms.
- Previous studies identified key proteins in coat morphogenesis and chromosome packaging.
Purpose of the Study:
- To apply immunofluorescence microscopy for visualizing subcellular protein localization during Bacillus subtilis sporulation.
- To investigate the roles of SpolVA and CotE in spore coat formation.
- To determine the localization and packaging mechanism of the spore chromosome and associated proteins.
Main Methods:
- Immunofluorescence microscopy was used to visualize protein localization.
- Studies involved wild-type and double mutant strains of Bacillus subtilis.
- Specific antibodies were employed to detect SpolVA, CotE, and alpha/beta-type small, acid-soluble proteins (SASPs).
Main Results:
- SpolVA assembles into a shell near the outer membrane during sporulation.
- CotE forms a second, larger shell, contributing to the outer coat layer.
- Alpha/beta-type SASPs are essential for packaging the spore chromosome into a distinct doughnut-like ring structure.
Conclusions:
- Immunofluorescence microscopy is a sensitive technique for high-resolution protein localization in bacteria.
- SpolVA and CotE play distinct roles in the sequential assembly of the spore coat.
- Alpha/beta-type SASPs are critical for organizing the spore chromosome into a compact, ring-like structure during Bacillus subtilis sporulation.