Emergence of active turbulence limits chemotaxis-induced collective condensation of bacteria

Collective bacterial condensation arises from positive feedback between the ability of bacteria to generate chemical gradients and their chemotactic ability to track those gradients, resulting in the spontaneous formation of local cell accumulations. Here, by following the bacterial condensation dynamics in uniform acidic environments, we show that condensation is critically constrained by the spontaneous emergence of correlated bacterial swimming. Under the unique conditions prevailing within the condensate—characterized by sharp cell-density gradients and the absence of physical boundaries—correlated bacterial motion leads to vortex-like cell motion with an additional substantial radial component directed down the cell-density gradient. Correlated bacterial motion leads, in turn, to local fluid motion that tends to broaden the condensate and expels non-chemotactic bacteria. However, when cells are embedded in a porous environment, correlated motion is suppressed, allowing spontaneous condensation to proceed further and form exceptionally dense bacterial accumulations. Overall, these findings highlight a previously unrecognized interplay between self-generated bacterial condensation and correlated swimming.