  A simulation approach to the stochastic growth of bacterial towers is
presented, in which a non-uniform and finite nutrient supply essentially
determines the emerging structure through elementary chemotaxis. The method is
based on cellular automata and we use simple, microscopic, local rules for
bacterial division in nutrient-rich surroundings. Stochastic nutrient
diffusion, while not crucial to the dynamics of the total population, is
influential in determining the porosity of the bacterial tower and the
roughness of its surface. As the bacteria run out of food, we observe an
exponentially rapid saturation to a carrying capacity distribution, similar in
many respects to that found in a recently proposed phenomenological
hierarchical population model, which uses heuristic parameters and macroscopic
rules. Complementary to that phenomenological model, the simulation aims at
giving more microscopic insight into the possible mechanisms for one of the
recently much studied bacterial morphotypes, known as "towering biofilm",
observed experimentally using confocal laser microscopy. A simulation
suggesting a mechanism for biofilm resistance to antibiotics is also shown.
