Self-Affinity for the Growing Interface of Bacterial Colonies

Abstract

We have investigated experimentally the self-affinity of bacterial colonies. We examined roughness exponent α for one-dimensional growing interfaces of colonies which belong to regions B and D in the morphological phase diagram of bacterial species Bacillus subtilis . Although macroscopically compact colony patterns are obtained in both B and D regions, microscopic growth mechanisms of their colony interfaces are quite different from each other. In the region B where the colony interface consists of many chains of bacterial cells that lie almost side by side and advances with clear long-range lateral correlations, we obtained α≃0.78 ±0.02. In the region D, however, where the interface is made of individual cells and advances rather locally through random pushes due to active movement of individual cells inside the colony, the value of α≃0.50 ±0.01 was obtained. The difference of values of the exponent α was thus found to be clearly attributed to that of microscopic growth mechanisms of colony interfaces.