Reversible Bacterial Depletion Aggregation and Restabilization by Water-Soluble Polymers

Area of Science:

• Soft Matter Physics
• Microbiology
• Biomaterials Science

Background:

• Depletion forces are critical in soft materials and biological systems.
• Their role in bacterial aggregation, impacting growth and infection, is increasingly recognized.
• Quantifying depletant concentrations for bacterial aggregation remains limited.

Purpose of the Study:

• To compare depletion aggregation of Escherichia coli by various macromolecules.
• To determine the concentration range for depletant-induced aggregation and restabilization.
• To understand how depletant size and type influence bacterial aggregation.

Main Methods:

• Investigated aggregation of flagella-free Escherichia coli.
• Tested depletants: hyaluronic acid, poly(acrylic acid) (PAA), guar, and albumin.
• Compared results with previous data for poly(ethylene oxide) and analyzed reversibility.

Main Results:

• Bacterial aggregation concentrations varied by two orders of magnitude across depletants.
• Guar induced aggregation below 0.03 wt%, while albumin required ~1 wt%.
• Polyanionic depletants aggregated bacteria below 0.01 wt% at low ionic strengths.
• Restabilization occurred at higher polymer concentrations, especially in dilute cell suspensions.

Conclusions:

• Macromolecular depletant size significantly impacts the concentration needed for bacterial aggregation.
• Depletion aggregation is reversible, distinguishing it from other mechanisms.
• Effective depletant volume fraction can predict minimum concentrations for aggregation.