Biased Lévy Walk Enables Light Gradient Sensing in Euglena gracilis

Area of Science:

• * Cellular and organismal biology
• * Biophysics
• * Microbial ecology

Background:

• * Photosensitive algae like Euglena gracilis navigate environments to optimize light exposure.
• * Stochastic movement patterns, including Lévy walks, are observed in various organisms for efficient searching.
• * Understanding Euglena gracilis navigation provides insights into eukaryotic sensory responses.

Purpose of the Study:

• * To investigate the navigation behavior of Euglena gracilis in confined spaces under varying light conditions.
• * To characterize the movement patterns and their relationship to light intensity and gradients.
• * To explore parallels between Euglena gracilis navigation and prokaryotic chemotaxis.

Main Methods:

• * Observation of Euglena gracilis movement in controlled laboratory settings.
• * Analysis of run-length distributions and their correlation with light intensity.
• * Development and validation of an agent-based model to simulate observed behaviors.

Main Results:

• * Euglena gracilis exhibits Lévy walk-like movement characterized by straight runs and abrupt turns.
• * Run durations are modulated by light intensity: extended for increasing light, shortened for decreasing light.
• * The agent-based model accurately replicates experimental observations of navigation under gradient lighting.

Conclusions:

• * Euglena gracilis employs a biased Lévy walk strategy to effectively navigate towards optimal light conditions.
• * This navigation strategy serves as a eukaryotic model for stochastic gradient ascent, similar to bacterial chemotaxis.
• * The study provides a quantitative understanding of phototaxis in Euglena gracilis and its underlying mechanisms.