  We present a new reaction-diffusion model for chiral branching growth of
colonies of the bacteria Paenibacillus dendritiformis. In our model the
bacteria are represented by a density field with non-linear diffusion and a
complex scalar field which represents bacterial orientation. The orientation
field introduces anisotropy into the flux of bacteria, representing
self-propulsion along their long axes. The model can also reproduce
tip-splitting growth of other strains (shorter bacteria) of the same species.
The model can capture changes of small number of bacteria, thus it can be used
to study the open question of transitions between tip-splitting and chiral
dendritic growth.
