Bacterial Growth in Stressed Environments

Trees and ferns often grow in fractal forms. Bacteria colonies can, too. But how?

First, the basic problem of fractal bacteria growth
Here are some examples
Can these growth patterns be explained by an alternative to DLA?
Chairal growth is a variation on fractal growth.
Rotex growth is another variation.
Fractal patterns also arise with fungus.

Are these patterns the result of simple physical processes, or do they represent self-organization and communication on many levels?
Certainly, different causes can produce the same effect: the existence of fractal bacteria colonies does not favor one mechanism over another.
But note 3 billion years of evolution have given Nature ample opportunity to discover and exploit purely physical processes.