Fluid dynamics of bacterial turbulence

Area of Science:

• Physics of complex fluids
• Microbiology
• Non-equilibrium statistical mechanics

Background:

• Self-sustained turbulent structures are common in biological fluids but lack theoretical explanation.
• Understanding these phenomena is crucial for fields ranging from developmental biology to engineered systems.

Purpose of the Study:

• To experimentally investigate active turbulence in concentrated bacterial suspensions.
• To develop and validate a minimal theoretical model for bacterial fluid dynamics.

Main Methods:

• Utilized velocimetry via imaging Bacillus subtilis cells and tracking colloidal tracers.
• Collected velocity statistics and correlations over a wide range of kinetic energies.
• Compared experimental data with a fourth-order vector-field theory for incompressible dynamics.

Main Results:

• Observed a decrease in fluid memory with increased bacterial swimming activity.
• Identified a linear scaling relationship between kinetic energy and enstrophy.
• Achieved quantitative agreement between experimental findings and the theoretical model.

Conclusions:

• The developed minimal theory accurately describes key aspects of active turbulence in bacterial suspensions.
• Bacterial activity fundamentally influences fluid properties like memory and energy distribution.
• This work provides a quantitative framework for understanding self-organized patterns in living fluids.