Mapping cell wall polysaccharides of living microbial cells using atomic force microscopy

Area of Science:

• Microbiology
• Biophysics
• Surface Science

Background:

• Understanding microbial cell surface composition is crucial for fields like immunology and drug development.
• Atomic Force Microscopy (AFM) offers high-resolution imaging and force measurement capabilities at the nanoscale.
• Specific ligand-receptor interactions on cell surfaces are key to biological processes.

Purpose of the Study:

• To quantify the specific binding forces between concanavalin A and mannan polymers on living yeast cells.
• To map the spatial distribution of mannan polysaccharides on the surface of Saccharomyces cerevisiae.
• To demonstrate the utility of functionalized AFM tips for probing molecular interactions on microbial surfaces.

Main Methods:

• Functionalized gold-coated AFM tips with concanavalin A using a cross-linker.
• Measured ligand-receptor binding forces between concanavalin A and mannan using AFM force spectroscopy.
• Employed AFM force volume mode to map the distribution of mannan on yeast cell surfaces.
• Utilized trigger mode with a constant pressing force (180 pN) to minimize non-specific adhesion.

Main Results:

• Specific binding forces between concanavalin A and mannan ranged from 75 to 200 pN.
• AFM force curves indicated polymer pull-off distances reaching several hundred nanometers.
• Mapping revealed a non-uniform distribution of mannan on the Saccharomyces cerevisiae cell surface.
• Low pressing force (180 pN) minimized non-specific adhesion, ensuring specific molecular recognition.

Conclusions:

• Functionalized AFM tips can effectively measure specific ligand-receptor binding forces on living microbial cells.
• The study successfully mapped the heterogeneous distribution of mannan on yeast cell surfaces.
• AFM force spectroscopy provides valuable insights into the molecular architecture and interactions of microbial cell surfaces.