Massive movements of birds and fish create large-scale patterns that can move around as if they were willing.Such mass movements are also seen in bacteria, and although there are many research reports, most of them were Escherichia coli, which is often used in laboratories.

　The research group focuses on soil bacteria (Flavobacterium Johnsonier).This bacterium was cultured on an agar plate, a solid surface used in microbial research, and the pattern produced by the population was recorded under an optical microscope for 30 hours every moment.Bacteria do not get over each other on the surface, so more bacteria collide, stick, and separate while moving dynamically.The resulting series of images was analyzed.

　In the surface movement of these bacteria, when the bacteria adhered to each other, they moved smoothly, and the left turn was biased.When the density becomes high, a small and uniform vortex pattern is formed.Gradually, it took in the surrounding vortices and formed a large vortex pattern (more than 500 million individuals) about 100 times its own size.Such a large vortex pattern and uniform counterclockwise rotation have not been reported so far.Some active bacteria on the outside seemed to drive the bacteria on the inside.Since this vortex is characteristic of a starved environment, it can be thought of as a survival strategy for bacterial populations that seek out nutrients like radar.

　It is currently unknown why bacteria tend to turn left when they become lumps.This bacterium is easy to generate various mutant strains by a genetic method.It is expected that it will be clarified by repeating experiments with various experimental materials and observation conditions.

Paper information:[Journal of Bacteriology] Large-scale vortices with dynamic rotation emerged from monolayer collective motion of gliding Flavobacteria