BACTERIAL FRACTAL GROWTH IN THE CONCENTRATION FIELD OF NUTRIENT

A Bacillus subtilis strain is found to grow through the diffusion-limited aggregation (DLA) process on agar plates. The organism is spotted on the agar plate containing a low concentration of peptone as a single nutrient and incubated at 35-degrees-C. The colony pattern grown on the plate surface is self-similar with the fractal dimension of 1.73 +/- 0.02. Bacterial DLA branches are shown to grow in a concentration field of nutrient from the fact that they grow predominantly in the direction of higher nutrient concentration. The colonial morphology varies with the nutrient and agar concentrations of an agar plate, including DLA, a round type, dense branching morphology (DBM), and a spreading without openings. Two neighboring colonies repulse each other in DLA and DBM types only. On an agar plate containing glycerol the colony becomes remarkably round, quite different from the DLA morphology.