Polar positional information in Escherichia coli spherical cells

Area of Science:

• Bacterial cell biology
• Microbial genetics
• Protein localization

Background:

• Shigella surface protein IcsA typically localizes to the old pole in rod-shaped Escherichia coli.
• In spherical mreB mutants, IcsA localizes to ectopic sites near MamK filaments, suggesting complex targeting mechanisms.

Purpose of the Study:

• To investigate the properties of cellular sites containing polar material in spherical E. coli.
• To understand the spatial relationship between IcsA localization and periplasmic structure.

Main Methods:

• Expression of IcsA-mCherry fusion proteins in spherical E. coli mutants (mreB and rodA-pbpA).
• Utilizing Green Fluorescent Protein (GFP) as a periplasmic marker via the Tat pathway.
• Confocal deconvolution microscopy to visualize protein localization and periplasmic distribution.

Main Results:

• Spherical E. coli cells exhibited zonal fluorescence with GFP, indicating an uneven periplasmic space.
• IcsA-mCherry was consistently found outside or at the edges of these GFP-defined periplasmic zones.
• This suggests IcsA localization is linked to specific structural or biochemical characteristics of the periplasm.

Conclusions:

• The periplasmic space in spherical E. coli is not uniform.
• Polar material, including IcsA, is targeted to regions with distinct periplasmic properties.
• This provides insight into the spatial organization and targeting of bacterial cell components.