Investigation of viscosity effects on bacteria collective motion using particle image velocimetry

Abstract

Swimming bacteria are known to display collective motion resulting from their flagella propulsion. Various models of such collective behavior have been proposed, and different motion patterns are also well-documented. However, no previous research has investigated how contrasts in fluid viscosity would influence the collective motion of swimming bacteria. In this paper, Particle Image Velocimetry (PIV), a commonly-used method to measure nonintrusive, instantaneous and whole-field velocity, is applied to visualize the swimming patterns and behavior of Escherichia coli and Vibrio alginolyticus. Firstly, various PIV post-processing tools are examined; next, different PIV conditions are tested and post-processing methods are optimized to best visualize bacteria collective motion; finally, the influence of viscosity contrast on bacteria behavior is investigated, and the swimming patterns that result from injecting active suspensions of bacteria with fluids of different viscosity are investigated.