Cell-cell adhesion control in multicellular assemblies under the influence of external fluid flow

Understanding the dynamics and viscoelastic properties of growing multicellular bacterial assemblies under external fluid flow is important for many applications. What behaviors are possible, and how they can be controlled with the strength and selectivity of cell-cell adhesins is largely unknown. Here we take a synthetic biology approach by controlling the expression of synthetic cell-cell adhesins in bacterial aggregates attached to a surface while subjecting these aggregates to external fluid flows. We experimentally characterize the phase space of possible behaviors of these aggregates based on flow conditions and adhesion strength. We identify a rich set of behaviors including cluster growth, cluster deformation, and intermittent cell shedding. We present a biophysical model explaining the observed behaviors. These results provide fundamental insights for active matter research, and will inform the behavior of clinical biofilms, the evolutionary constraints of multicellular life, and have applications like active biomaterials, among others.