Hydrodynamic interaction leads to the accumulation of Chlamydomonas reinhardtii near a solid-liquid interface

TL;DR

This study investigates how hydrodynamic interactions cause Chlamydomonas reinhardtii cells to accumulate near solid-liquid interfaces, combining real-time tracking microscopy with a simplified force dipole model to explain the phenomenon.

Contribution

The paper introduces a new three-dimensional tracking method and a simplified hydrodynamic model to explain cell accumulation near solid surfaces, specifically for C. reinhardtii.

Findings

C. reinhardtii cells tend to accumulate near solid-liquid interfaces.

Hydrodynamic interactions are key to understanding this accumulation.

A simplified force dipole model explains the observed behavior.

Abstract

The physical mechanism of microbial motion near solid-liquid interfaces is crucial for understanding various biological phenomena and developing ecological applications. However, limited works have been conducted on the swimming behavior of C. reinhardtii, a typical "puller" type cell, near solid surfaces, particularly with varying and conflicting experimental observations. Here, we investigate the swimming behavior of C.reinhardtii using a three-dimensional real-time tracking microscopy system both near a solid-liquid interface and in the fluid bulk region. We explore the relationships between the cell density, swimming speed and orientation with respect to the distance from the solid-liquid interface, confirming the phenomenon of C. reinhardtii accumulation near the solid-liquid interface. Based on the traditional definitions of "pusher" and "puller" cells, we propose a simplified model consisting of two pairs of mutually perpendicular force dipoles for C. reinhardtii. This model is employed to analyze the complex hydrodynamic interactions between C. reinhardtii and the solid surface, providing a potential theoretical explanation for the observed accumulation phenomenon at the solid-liquid interface.