Bacterial colonies can develop chiral morphology in which the colony consists of twisted branches, all with the same handedness. Microscopic observations of the chiral growth are presented. We propose that the observed (macroscopic) chirality results from the microscopic chirality of the flagella (via handedness in tumbling) together with orientation interaction between the bacteria. The above assumptions are tested using a generalized version of the communicating walkers model.

• Received 28 September 1994

DOI:https://doi.org/10.1103/PhysRevLett.75.2899