Swimming microorganisms (bacteria, algae) are surrounded by flows generated by their flagella. These flows cause propulsion and lateral attractive forces between organisms. In concentrated populations of swimming bacteria remarkable collective dynamics emerge: spontaneously developing fast moving evanescent polar domains. Microflows collectively
generated by many flagella also function to enormously enhance transport of molecules associated both with life processes and inter-organism signalling. Related phenomena are symmetry-breaking behaviors of individual bacteria, e.g. flagella-flipping reversals of swimming direction and rotation, and maintenance of circulating swimming direction within small droplets.
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