Optical confinement and rectification of photokinetic bacteria by feedback controlled light patterns

The bacteria Escherichia coli can be genetically engineered to swim with a light controllable speed, which turns them into the excellent tool to investigate the physics of active systems. We demonstrate a method to guide and optically confine these photokinetic bacteria towards any desired region of space. We implement a feedback loop in which the projected light pattern is determined by geometric transformations of a cell density image captured at an earlier time. With these dynamic light patterns, we are able to only boost bacteria that move in a chosen direction, which results in a directed flow of cells with an associated velocity field that can be controlled in amplitude and direction as predicted by an analytic run and tumble model. We extend the method further and use it to create large formations of confined bacteria by collecting the most motile cells and trapping them in high density and high activity formations stably over long time periods, differently from other methods that gather bacteria in low motility areas. Precisely guiding and trapping large populations of bacteria can present relevant applications in microfluidic devices, as well as it is highly interesting for the fundamental study of active matter systems and their statistical mechanic properties.