Formation Mechanism of Periodically Growing Patterns

点击翻译按钮获取中文摘要

We have investigated experimentally the periodic pattern formation in order to elucidate the growth mechanism. We have especially focused our attention on the concentric ring colonies of bacteria and concentric ring patterns produced by crystal growth.In the case of bacterial colonies we mainly used Bacillus subtilis as sample bacterial species. We have confirmed that the concentric ring colonies reflect the periodic change of the bacterial cell motility between motile cell state (migration period) and immotile cell state (consolidation period). We conclude that this periodic change is macroscopically determined neither by microbiological factors (i.e., biological clock) nor by chemical factors (chemotaxis as inhibitor). And our experimental results strongly suggest that the essential factor for the change of bacterial cell motility during the concentric ring colony formation is the local cell density. Namely we propose the existence of the thresholds of cell density for the initiation of both migration and consolidation periods. In the meantime we found that bacterial species Serratia marcescens and Escherichia coli also produce concentric ring colonies under appropriate conditions. We now believe that the formation of concentric ring colonies is pretty common in the bacterial world.In the case of crystal growth we focused our attention on the concentric ring formation of L-ascorbic acid grown from methanol solution. In order to elucidate the growth mechanism of the concentric ring patterns we first established the morphological diagram in the two-parameter space, i.e., solute concentration-ambient humidity and temperature-ambient humidity. We found that the most influential factor for the pattern selection including concentric ring pattern is the ambient humidity.