Supplemental material to:

1.1 Complex modular organization When grown on semi-solid surfaces, P. vortex organize its colonies by generating rotating modules (termed vortices), each consisting of many cells, which are used as building blocks for the colony as a whole [1-17] as is illustrated in Figure S1. Each vortex is composed of many cells that swarm collectively around their common center at about 10 micron/sec (see Movie S1). The vortices vary in size from tens to millions of bacteria, according to their location in the colony. The cells in the vortex replicate, and the vortex expands in size and moves outward as a unit, leaving behind a trail of motile but usually non-replicating cells – the vortex branch. The dynamics of the vortices is quite complicated and includes attraction, repulsion, merging and splitting of vortices. Yet, from this complex, seemingly chaotic dynamics, a colony with complex but non-arbitrary organization emerges. The bacteria in each vortex also have high length variability. Transmission electron microscope (TEM) observations revealed that the elongated cells have several chromosomes.