Should I stay or should I go? Spatio-temporal dynamics of bacterial biofilms in confined flows

Most bacteria live in sessile biofilms that colonize the confined channels, pores and crevices of natural and engineered structures. In these environments, flow delivers nutrients necessary for growth while simultaneously generating mechanical stresses that cause detachment from surfaces. Bacteria, in turn, colonize flow passages, increasing hydraulic resistance and modifying transport properties. Although the importance of advective transport and hydrodynamic forces on bacterial populations is well established, the complex feedback mechanisms governing biofilm development in confined geometries remain poorly understood. Here, we study how couplings between flow and bacterial development control the spatiotemporal dynamics of Pseudomonas aeruginosa in microchannel flows. We demonstrate that nutrient availability primarily drives the longitudinal distribution of biomass along the channel, while competition between growth and flow-induced detachment controls the transverse distribution and temporal dynamics. We find that biofilms undergo successive cycles of sloughing and regrowth, causing persistent fluctuations in the hydraulic resistance and biomass that prevent the system from ever reaching a true steady state. Our results indicate that these self-sustained fluctuations are a signature effect in confined flows, originating from a pressure build-up as growing bacteria obstruct flow paths. We further show that the sloughing dynamics can be described as a jump stochastic process with gamma-distributed interevent times, analogous to other bursting events such as earthquakes or avalanches. This stochastic framework provides a quantitative approach to characterizing the inherent randomness and apparent irreproducibility of biofilm experiments, opening new avenues for predictive modeling of biofilms in confined systems.