Bacterial population inversion near a hydrodynamic blackhole

We present a 2-dimensional enclosed microfluidic environment that utilizes concentric rings of funnel ratchets which act like gravity to direct motile bacteria (E.coli) towards an exit hole, entry into which irreversibly sweeps the bacteria away via hydrodynamic flow. We show that the disappearance of bacteria and their signaling molecules near this hydrodynamic ``black hole'' triggers the emergence of a population inversion where the remaining bacteria collectively move away from the black hole in spite of the presence of increased nutrients within the flow stream and the effective gravity force field. We study the fundamental significance of cell-cell communication in these phenomena by simulating different Brenner-Patlak-Keller-Segel models including those with and without a direct intercellular information flow, through analytical and numerical approaches. This experiment reveals how local bacteria density and signaling chemicals allow bacteria to can gain global information about their surrounding, and collectively avoid a hydrodynamic event horizon.