Curli production enhances clay-E. coli aggregation and sedimentation

Area of Science:

• Microbiology
• Environmental Science
• Biophysics

Background:

• Curli are extracellular amyloid fibrils produced by enteric bacteria, crucial for biofilm formation.
• Bacterial interactions with environmental particles like clay influence microbial fate and transport.
• Understanding these interactions is vital for environmental microbiology and biotechnology.

Purpose of the Study:

• To investigate the impact of curli production on the aggregation behavior of bacteria and their interactions with clay minerals.
• To elucidate the physical and chemical factors governing bacteria-clay complex formation in the presence of curli.

Main Methods:

• Gradient-sedimentation experiments
• Lumisizer measurements
• Bright-field and electron microscopy (SEM)
• Varying ionic strength and clay types (montmorillonite, kaolinite)

Main Results:

• Curli-producing bacteria formed dense, spontaneously settling aggregates (10-50 μm).
• Curli-deficient bacteria remained dispersed as individual cells, behaving predictably with clay according to DLVO theory.
• Curli-producing bacteria-clay suspensions were unstable, showing extensive interactions and distinct aggregate morphologies (e.g., clay coating or embedding).

Conclusions:

• Curli significantly enhance bacterial aggregation and alter interactions with clay minerals.
• Bacterial surface appendages like curli are critical factors in bacterial-clay complex formation and environmental transport.
• These findings have implications for understanding microbial behavior in aquatic and soil environments.