Phototgyrotactic concentration of a population of swimming microalgae across a porous layer

TL;DR

This study investigates how phototaxis influences the migration and concentration of microalgae in a controlled environment, demonstrating that a porous layer can trap and concentrate microalgae above it, with implications for biotechnology and ecology.

Contribution

We demonstrate how a porous layer can control microalgae concentration by exploiting phototaxis, providing new insights into microalgae behavior and potential biotechnological applications.

Findings

Phototaxis affects microalgae suspension stability.

Porous layer prevents sinking, concentrates microalgae.

Potential applications in biotechnological processes.

Abstract

The light environment controls the swimming of microalgae through a light-seeking and avoiding behaviour, which is known as phototaxis. In this work, we exploit phototaxis to control the migration and concentration of populations of the soil microalga {\it Chlamydomonas reinhardtii}. By imaging a suspension of these microalgae in a cuvette illuminated from above by blue light, we study how phototaxis changes the stability of the suspension and demonstrate how a thin, porous layer at the top of the cuvette prevents phototaxing microalgae from sinking, leading to the up-concentration of the microalgae in the region above the porous layer. We discuss the potential implications of our findings for microalgae in biotechnological applications and the natural environment.