Folded chromosomes of vegetative Bacillus subtilis: composition and properties

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Bacterial DNA is organized into nucleoids, influencing gene expression and replication.
• Understanding the structure of folded DNA is crucial for deciphering cellular processes.

Purpose of the Study:

• To isolate and characterize folded DNA (nucleoids) from Bacillus subtilis.
• To investigate the effect of lysis salt concentration on nucleoid structure and composition.
• To analyze the protein components associated with the folded bacterial chromosome.

Main Methods:

• Isolation of folded DNA from Bacillus subtilis using differential salt concentrations (0.2 M NaCl vs. 1 M NaCl).
• Sedimentation analysis to determine nucleoid size (Svedberg units).
• Biochemical analysis of nucleoid composition (RNA, lipids, proteins).
• Electrophoresis and biochemical treatments to identify associated proteins.

Main Results:

• Two distinct nucleoid structures were obtained: slow-sedimenting (1600-2000 S) with 1 M NaCl and fast-sedimenting (3500-4000 S) with 0.2 M NaCl.
• High yields (80-90%) of folded DNA were achieved.
• Nucleoids differed in protein and lipid proportions but contained similar RNA amounts.
• A dominant 36,000 MW polypeptide remained associated with DNA, suggesting a structural role.

Conclusions:

• Salt concentration during lysis significantly impacts Bacillus subtilis nucleoid structure and sedimentation properties.
• The isolated folded DNA structures provide insights into bacterial chromosome organization.
• Specific proteins, including a prominent 36,000 MW polypeptide, are integral to folded chromosome structure.