Chirality-induced bacterial rheotaxis in bulk shear flows.

Area of Science:

• Microbial transport phenomena
• Fluid dynamics of microorganisms
• Biophysics of bacterial motility

Background:

• Bacterial interaction with fluid flows is critical for environmental navigation and biotechnological applications like cell sorting.
• Understanding bacterial rheotaxis in shear flows is essential for predicting their collective behavior and transport.
• Previous studies lacked a comprehensive understanding of the interplay between bacterial properties and flow dynamics.

Purpose of the Study:

• To comprehensively investigate the transport of motile bacteria in shear flows.
• To elucidate the physical mechanisms and key parameters governing bacterial rheotaxis.
• To bridge experimental, numerical, and theoretical analyses for a complete understanding.

Main Methods:

• High-accuracy experimental measurements of bacterial velocity and orientation distributions across various flow rates.
• Numerical simulations using a kinematic model incorporating stochastic and microhydrodynamic properties, including flagellar chirality.
• Theoretical analysis to derive scaling laws for rheotactic velocity and explain reorientation dynamics.

Main Results:

• Experimental data showed excellent agreement with simulation results, validating the kinematic model.
• Identified scaling laws for average rheotactic velocity at moderate shear rates, dependent on a chirality parameter.
• Explained reorientation dynamics and saturation at high shear rates through the marginal stability of a fixed point.

Conclusions:

• Achieved a full understanding of the physical mechanisms driving bacteria bulk rheotaxis in shear flows.
• Demonstrated the critical role of flagellar chirality and microhydrodynamics in bacterial transport.
• Findings are relevant for microfluidic applications and understanding bacterial behavior in complex environments.