Co-zorbs: Motile, multispecies biofilms aid transport of diverse bacterial species

Biofilms are three-dimensional structures containing one or more bacterial species embedded in extracellular polymeric substances. Although most biofilms are stationary, Flavobacterium johnsoniae forms a motile spherical biofilm called a zorb, which is propelled by its base cells and contains a polysaccharide core. Here, we report formation of spatially organized, motile, multispecies biofilms, designated "co-zorbs," that are distinguished by a core-shell structure. F. johnsoniae forms zorbs whose cells collect other bacterial species and transport them to the zorb core, forming a co-zorb. Live imaging revealed that co-zorbs also form in zebrafish, thereby demonstrating a new type of bacterial movement in vivo. This discovery opens new avenues for understanding community behaviors, the role of biofilms in bulk bacterial transport, and collective strategies for microbial success in various environments. Significance StatementThis paper reports the discovery of co-zorbs, which are spherical aggregates of bacteria that move and transport other bacteria. Zorbs move toward other bacteria and collect them in a manner reminiscent of phagocytes. Once inside the zorb, the new species form a striking, organized core. The discovery of co-zorbs introduces an entirely new type of bacterial movement and transport involving cooperation among bacterial species. Co-zorbs have potential for engineering microbial systems for biotechnology applications and for managing spread of bacterial pathogens in their hosts.