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 $C.\mathit{reinhardtii}$, a typical “puller” type cell, near solid surfaces, particularly with varying and conflicting experimental observations. Here, we investigate the swimming behavior of $C.\mathit{reinhardtii}$ 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 $C.\mathit{reinhardtii}$ accumulation near the solid-liquid interface. Based on the traditional definitions of “pusher” and “puller” cells, we propose a simplified model consisting of a pair of mutually perpendicular force dipoles for $C.\mathit{reinhardtii}$. This model is employed to analyze the complex hydrodynamic interactions between $C.\mathit{reinhardtii}$ and the solid surface, providing a potential theoretical explanation for the observed accumulation phenomenon at the solid-liquid interface.

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• Biological fluid dynamics
• Cellular organization, physiology & dynamics
• Low Reynolds number swimmers