Pattern Formation of Bacterial Colonies by Escherichia coli

概要

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We have studied the morphological diversity and change in bacterial colonies, using the bacterial species Escherichia coli, as a function of both agar concentration $C_{\text{a}}$ and nutrient concentration $C_{\text{n}}$. We observed various colony patterns, classified them into four types by pattern characteristics and established a morphological diagram by dividing it into four regions. They are regions A [diffusion-limited aggregation (DLA)-like], B (Eden-like), C (concentric-ring), and D (fluid-spreading). In particular, we have observed a concentric-ring colony growth for E. coli. We focused on the periodic growth in region C and obtained the following results: (i) A colony grows cyclically with the growing front repeating an advance (migration phase) and a momentary rest (consolidation phase) alternately. (ii) The growth width $L$ and the bulge width $W$ in one cycle decrease asymptotically to certain values, when $C_{\text{a}}$ is increased. (iii) $L$ does not depend on $C_{\text{n}}$, while $W$ is an increasing function of $C_{\text{n}}$. Plausible mechanisms are proposed to explain the experimental results, by comparing them with those obtained for other bacterial species such as Proteus mirabilis and Bacillus subtilis.
2009-07-15