Microstructural and Rheological Transitions in Bacterial Biofilms

Area of Science:

• Microbiology
• Biophysics
• Materials Science

Background:

• Biofilms are bacterial communities encased in an extracellular matrix (ECM), crucial for their architecture and mechanical stability.
• Biofilms can be physically modeled as colloidal gels, with cells as particles in a polymeric ECM.
• The impact of ECM on biofilm cellular packing fraction (ϕ) and viscoelasticity is not well understood.

Purpose of the Study:

• To investigate the correlation between biofilm structure, specifically cellular packing fraction (ϕ), and viscoelastic behavior.
• To explore the role of exopolysaccharide (EPS) in modulating biofilm structure and rheological properties.

Main Methods:

• Utilized wild-type (WT) Pantoea sp. and a mutant (ΔUDP) with reduced exopolysaccharide production.
• Quantified cellular packing fraction (ϕ) in biofilms.
• Characterized viscoelastic responses using rheological measurements.
• Employed co-culturing techniques to modulate biofilm ϕ and observe structural transitions.

Main Results:

• ΔUDP biofilms showed a seven-fold increase in ϕ compared to WT, exhibiting a colloidal glass-like structure.
• WT biofilms displayed weak gel rheological signatures, while ΔUDP biofilms showed glass-like signatures.
• Modulating ϕ through co-culturing induced transitions from weak gel to strong gel and colloidal glass states.

Conclusions:

• Exopolysaccharide plays a critical role in mediating structural transitions within biofilms.
• A direct correlation exists between biofilm structure (specifically ϕ) and its emergent viscoelastic response.
• This study provides a physical framework for understanding biofilm mechanics based on colloidal principles.