The cell cycle of Bacillus subtilis as studied by electron microscopy

Area of Science:

• Microbiology
• Cell Biology
• Molecular Biology

Background:

• Understanding bacterial cell cycle progression is crucial for comprehending microbial growth and division.
• Bacillus subtilis serves as a model organism for studying fundamental bacterial processes.

Purpose of the Study:

• To elucidate the temporal sequence of key events in the Bacillus subtilis cell cycle.
• To precisely determine the duration of DNA replication and segregation phases.

Main Methods:

• Exponentially growing Bacillus subtilis cells were analyzed using agar filtration for cell cycle staging by length.
• DNA replication timing was quantified via radioautography of tritiated thymidine pulse-labeled cells.
• Cell morphology and nucleoplasmic body segregation were examined using thin section electron microscopy.

Main Results:

• The DNA replication period in Bacillus subtilis was determined to be 45 minutes, with non-synthesis periods of approximately 10 minutes before and after.
• DNA replication and segregation were observed to occur concurrently, with segregation completing shortly after replication.
• Cell division initiation was noted at approximately 20 minutes post-cell birth, and cell separation commenced around 45 minutes, preceding septum completion.

Conclusions:

• The Bacillus subtilis cell cycle is characterized by tightly coordinated DNA replication, segregation, and division processes.
• Segregation of the two B. subtilis genomes is closely linked to and follows DNA replication.
• Cell division and separation events are initiated early in the cell cycle, with separation occurring before the completion of cell division.