Two dimensional bacterial turbulence at a liquid-air interface

Active turbulence is a ubiquitous signature of active matter systems, as observed in dense suspensions of E. coli bacteria and cytoskeleton-motor systems. In experiment, 2D bacterial turbulence is normally formed in a thin layer of liquid near a substrate, or between two liquids phases. Here, we use Serratia marcescens bacteria that swim at a water-air interface to study 2D bacterial turbulence. By cell culture, Serratia bacterial with body length from 1 to 10um can be obtained. By using a microbubble assay, the thickness of the liquid layer can be adjusted from 0 to several mm. In low-viscosity aqueous solutions, the energy spectrum E(k) of 2D turbulence shows a universal power-law scaling that is independent of cell length and liquid thickness. At the meantime, we observe transition from nematic-order to turbulence in 2D bacterial suspension.