Sharp turns and gyrotaxis modulate surface accumulation of microorganisms.

Area of Science:

• Microbiology
• Biophysics
• Fluid Dynamics

Background:

• Microorganism accumulation at surfaces is crucial for processes in confined spaces.
• Current models attribute this to changes in swimming speed and angular velocity from cell-wall contact and hydrodynamics.

Purpose of the Study:

• To investigate the swimming behavior of Heterosigma akashiwo near vertical and horizontal boundaries.
• To understand the mechanisms driving microorganism accumulation at surfaces.

Main Methods:

• Measured swimming trajectories of Heterosigma akashiwo near rigid boundaries.
• Developed an individual-based model incorporating measured swimming parameters.

Main Results:

• Increased probability of sharp turns near vertical walls, altering speed, angular velocity, and rotational diffusivity.
• Observed amplified cell accumulation beneath horizontal walls due to cell-wall interaction.
• Standard hydrodynamic models could not fully explain the observed behaviors.

Conclusions:

• Cell-wall interactions, particularly flagellum contact, induce complex behaviors not captured by current models.
• An individual-based model using measured distributions accurately predicts cell concentration.
• Findings enhance understanding of microorganism distribution influenced by gyrotaxis and cell-wall contact.