Auto-chemotactic micro-swimmer suspensions: modeling, analysis and simulations

TL;DR

This paper models and analyzes how auto-chemotactic micro-swimmer suspensions behave under fluid flows, revealing instabilities and complex aggregation dynamics through linear analysis and nonlinear simulations.

Contribution

It introduces a coupled hydrodynamic and chemotaxis model for micro-swimmer suspensions, highlighting the impact of fluid flows on aggregation and stability.

Findings

Chemotactic aggregation is influenced by hydrodynamic interactions.

Pushers and pullers exhibit different instability behaviors.

Hydrodynamics can suppress or modify chemotactic clustering.

Abstract

Microorganisms can preferentially orient and move along gradients of a chemo-attractant (i.e., chemotax) while colonies of many microorganisms can collectively undergo complex dynamics in response to chemo-attractants that they themselves produce. For colonies or groups of micro-swimmers we investigate how an "auto-chemotactic" response that should lead to swimmer aggregation is affected by the non-trivial fluid flows that are generated by collective swimming. For this, we consider chemotaxis models based upon a hydrodynamic theory of motile suspensions that are fully coupled to chemo-attractant production, transport, and diffusion. Linear analysis of isotropically ordered suspensions reveals both an aggregative instability due to chemotaxis that occurs independently of swimmer type, and a hydrodynamic instability when the swimmers are "pushers". Nonlinear simulations show nonetheless that hydrodynamic interactions can significantly modify the chemotactically-driven aggregation dynamics in suspensions of "pushers" or "pullers". Different states of the dynamics resulting from these coupled interactions in the colony are discussed.