Characteristic patterns of expansion were generated by bacterial cell populations of Serratia marcescens on media with different concentrations of nutrient and agar. These patterns were classified as Eden-like, dense-branching-morphology-like, flower-like, concentric ring-like and diffusion-limited aggregation-like. Although flower-like was specific to Serratia marcescens, the other patterns were exhibited by Bacillus subtilis. Through macro- and microscopic tracing of the processes generating these patterns, physico-chemical principles of bacterial growth, collaborative and independent properties of bacteria, structural organization for population expansion, and the division of labor among bacterial cells (i.e., wall composer, pressure generator, and logistic supporter) were brought to light.
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