Crowding limits relative bacterial surface accumulation with density-induced effective heating

The accumulation of microswimmers near walls has been studied for decades. While hydrodynamics and single-cell kinematics are well-explored, the role of cell-cell interactions remains understudied. However, in realistic, crowded environments such as the human gut, these interactions can be just as crucial. Here, we demonstrate that they actively weaken bacterial surface accumulation. Analysis of entrapped cell tracks reveals that crowding enhances orientational fluctuations, which increase the effective rotational diffusion and facilitate wall escape. A minimal model shows that this collective effect is equivalent to raising the system's effective temperature with density.