Active Dispersal and Rolling Motility in Bacterial Aggregates

Microorganism dispersal is fundamental to their abundance in nature and plays a crucial role in pathogen transmissions. In general, active dispersals are attributed to the movements of self-powered planktonic cells, and sessile cells can only be transported passively through flow entrainment for their lack of powering organelles. Here, we report an active means of dispersal employed by aggregates of motile and sessile cells. The sessile cells of bacterium Caulobacter crescentus can form spherical rosette colonies, within which a small proportion can grow active flagella and enable whole-rosette motility. We show that these rosettes disperse actively both in bulk water and near the solid-liquid interface. In particular, the proximity of a self-powered rosette to the solid surface promotes a rolling movement, leading to its persistent transportation along the solid boundary. The active dispersal of these rosettes demonstrates an exclusive mode of colonial transportation that is based on the division of labor. Such aggregates are potentially adaptive for more efficient colonial transport and may provide guidance for biomimetic engineering of microsystems.