Self-organization of swimmers drives long-range fluid transport in bacterial colonies

Microbes commonly live in structured communities that affect human health and influence ecological systems. Colony mode of bacterial growth on solid substrates (e.g. food products) is closely related to biofilm development, and it is a main approach to study structured microbial communities. Heterogeneous populations, such as non-motile and motile populations, often coexist in bacteria colonies. Here we discovered that motile cells in sessile colonies of peritrichously flagellated bacteria can self-organize into motile bands that can drive long-range fluid transport at a constant speed of ~30 μm/s, providing a stable high-speed avenue for material transport at the colony scale. These findings present a unique form of large-scale self-organization and active transport in bacterial colonies.