Phototaxis beyond turning: persistent accumulation and response acclimation of the microalga Chlamydomonas reinhardtii

TL;DR

This study quantitatively investigates the long-term phototactic behavior of Chlamydomonas reinhardtii, revealing how light exposure history influences cell navigation and how photosynthesis modulates this response over time.

Contribution

It provides the first detailed analysis of long timescale phototactic motility and adaptation in Chlamydomonas reinhardtii, linking photosynthesis to navigation strategies.

Findings

Phototactic response modulates over tens of seconds.

Cells efficiently expose themselves to light through their strategy.

Photosynthesis controls the phototactic adaptation process.

Abstract

Phototaxis is an important reaction to light displayed by a wide range of motile microorganisms. Flagellated eukaryotic microalgae in particular, like the model organism Chlamydomonas reinhardtii, steer either towards or away from light by a rapid and precisely timed modulation of their flagellar activity. Cell steering, however, is only the beginning of a much longer process which ultimately allows cells to determine their light exposure history. This process is not well understood. Here we present a first quantitative study of the long timescale phototactic motility of Chlamydomonas at both single cell and population levels. Our results reveal that the phototactic strategy adopted by these microorganisms leads to an efficient exposure to light, and that the phototactic response is modulated over typical timescales of tens of seconds. The adaptation dynamics for phototaxis and chlorophyll fluorescence show a striking quantitative agreement, suggesting that photosynthesis controls quantitatively how cells navigate a light field.