Development of concentric zones in the Proteus swarm colony.

Two main mechanisms of concentric ring formation in cultures of Proteus species are described. One of these is the classically accepted method, wherein rings are produced as the advance of the swarm stops and recommences. In the other, the ring is produced as a fold inside the colony. These are considered to be extremes of a spectrum of growth types, the common feature being that rings are formed by piling-up of growth, and this process is not always directly correlated with morphological change in the individual bacteria, or with cessation of advance of the swarm. The validity of the presently accepted theories of ring formation and swarming in general are thus called into question.