Distinct constrictive processes, separated in time and space, divide caulobacter inner and outer membranes

Area of Science:

• Microbiology
• Cell Biology
• Biophysics

Background:

• Bacterial cell division is crucial for microbial life.
• Caulobacter crescentus is a model organism for studying cell cycle and division.
• Understanding the mechanisms of cell envelope constriction is key to bacterial reproduction.

Purpose of the Study:

• To characterize the terminal stages of Caulobacter crescentus cell division.
• To investigate the spatial and temporal separation of inner and outer membrane constriction.
• To examine protein diffusion dynamics during cell division.

Main Methods:

• Cryoelectron microscope tomography (cryo-EM) to visualize cell division structures.
• Fluorescence loss in photobleaching (FLIP) assays to track protein diffusion and compartmentalization.

Main Results:

• Cryo-EM revealed sequential constriction of the inner membrane (IM) followed by the outer membrane (OM), differing from septum-forming bacteria.
• Cytoplasmic compartmentalization occurred 18 minutes before cell separation.
• Small membrane tethers (60 nm) were observed during late-stage IM and OM constriction.
• FLIP experiments demonstrated free diffusion of membrane-bound and periplasmic proteins through the FtsZ ring during most of the constriction process.

Conclusions:

• Caulobacter crescentus employs a unique cell division mechanism involving temporally and spatially separated IM and OM constrictions.
• The FtsZ ring permits significant protein diffusion throughout the division process.
• This study provides novel insights into the biophysical mechanisms of bacterial cytokinesis.