Long-Term Visualization of Micro Vortices in Bacillus Subtilis Bacterial Biofilm on Agar Plate using Particle Image Velocimetry

Abstract

The collective dynamics of bacteria has a crucial role in the development of biofilm. Although the behavior of the fluidic biofilm was studied by many research groups, detailed mechanics of its motion still remains elusive. Previously, we developed a method for visualization of vortical flow in the Bacillus Subtilis (B. subtilis) colony using 200-nm fluorescent microbeads, which were initially embedded in the agar plate and distributed spontaneously at the upper surface of the growing colony. Here, we conducted a long-term live imaging of B. subtilis colony with the fluorescent beads and obtained high-resolution velocity maps of microscale vortices in the biofilm using particle image velocimetry (PIV). At the tip of the colony, a distinct periodic fluctuation of average speed and vorticity revealed by Micro-PIV analysis was correlated with switching between bacterial swarming and growth phases. Our advanced imaging tool helps to explain the effect of micro vorticies in the biofilm on the collective dynamics of bacteria.