Shaving and breaking bacterial chains with a viscous flow

Area of Science:

• Microbiology and Food Science
• Biophysics and Fluid Dynamics

Background:

• Food and ferment manufacturing processes like spray-drying expose bacteria to viscous stresses.
• Bacterial adhesion is crucial for functionality but can be affected by physical forces.
• Lactobacillus rhamnosus GG (LGG) utilizes pili for strong adhesion to substrates like beta-lactoglobulin.

Purpose of the Study:

• To investigate the impact of viscous flow on bacterial adhesion and cell organization.
• To understand how shear rates in manufacturing affect bacterial cell structures and adhesive capabilities.
• To model the relationship between fluid dynamics, surface forces, and bacterial chain integrity.

Main Methods:

• Experimental approach using Lactobacillus rhamnosus GG (wild type) and mutant strains.
• Application of repeated high shear-rate flows to assess changes in adhesion and cell organization.
• Numerical and analytical modeling of Stokes equations for fluid flow around bacterial chains.

Main Results:

• High shear rates reduced LGG WT adhesive abilities by up to 20%.
• Bacterial chains fragmented into 2-cell chains at low shear rates and single cells at very high shear rates.
• Modeling showed longer chains experience higher surface tractions, especially at extremities, while inner cells are protected.

Conclusions:

• Viscous stresses in food processing can impair bacterial adhesion and disrupt cell chains.
• Bacterial chain rupture may serve as a protective mechanism, preserving adhesive functionality.
• Hydrodynamic interactions within chains influence the distribution of forces on individual cells.