Structural changes in the nucleoid of Bacillus subtilis at low temperature

Area of Science:

• Microbiology
• Cell Biology
• Microscopy Techniques

Background:

• The nucleoid, the region containing the genetic material in bacteria, has a complex structure influenced by fixation methods.
• Traditional fixation techniques like OsO4 may alter the native appearance of the bacterial nucleoid.
• Understanding nucleoid morphology is crucial for comprehending bacterial physiology and DNA organization.

Purpose of the Study:

• To investigate the external shape of the Bacillus subtilis nucleoid using a novel electron microscopy technique.
• To determine how temperature and buffer conditions affect nucleoid structure.
• To explore the relationship between nucleoid shape changes and bacterial membrane fluidity.

Main Methods:

• Employed rapid freezing and substitution fixation, a new electron microscopic technique.
• Examined Bacillus subtilis strain w23 cells in both log and stationary growth phases.
• Assessed nucleoid morphology under varying temperature (0-10°C) and salt buffer conditions.

Main Results:

• The nucleoid appeared as a ribosome-free, dispersed area in the cytoplasm with the new technique, differing from OsO4-fixed cells.
• At low temperatures (0-10°C) in a high-salt buffer, the nucleoid adopted a highly concentrated, central cytoplasmic shape.
• These temperature-induced structural changes were contingent on the presence of a high-salt buffer.

Conclusions:

• Rapid freezing and substitution fixation offers a different perspective on Bacillus subtilis nucleoid structure.
• Bacterial nucleoid shape is dynamic and sensitive to environmental conditions like temperature and salt concentration.
• Observed nucleoid structural changes likely correlate with alterations in membrane fluidity at low temperatures.