Formation Mechanism of Periodically Growing Patterns

我们已经在实验上研究了周期性图案的形成，以阐明生长机制。我们特别关注了细菌的同心环菌落和晶体生长产生的同心环图案，在细菌菌落的情况下，我们主要使用枯草芽孢杆菌作为样品细菌种。我们已经证实，同心环形菌落反映了细菌细胞运动性在运动细胞状态（迁移期）和不运动细胞状态（巩固期）之间的周期性变化。我们得出结论，这种周期性变化既不是由微生物因素（即，生物钟），也不是由化学因素（趋化性作为抑制剂）。实验结果表明，在同心环集落形成过程中，局部细胞密度是影响细菌细胞运动性变化的根本因素。也就是说，我们提出了细胞密度阈值的存在，为迁移和巩固期的启动。同时我们发现粘质沙雷氏菌和大肠杆菌在适当的条件下也能产生同心环菌落。我们现在认为同心环菌落的形成在细菌世界中是很常见的。在晶体生长的情况下，我们把注意力集中在从甲醇溶液中生长的L-抗坏血酸的同心环形成。为了阐明同心环图案的生长机制，我们首先建立了双参数空间中的形态图，即，溶质浓度-环境湿度和温度-环境湿度。我们发现，最有影响力的因素的图案选择，包括同心环图案是环境湿度。

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.