Bacterial cells can self-organize into structured communities at fluid–fluid interfaces. These soft, living materials composed of cells and extracellular matrix are called pellicles. Cells residing in pellicles garner group-level survival advantages such as increased antibiotic resistance. The dynamics of pellicle formation and, more generally, how complex morphologies arise from active biomaterials confined at interfaces are not well understood. Here, using Vibrio cholerae as our model organism, a custom-built adaptive stereo microscope, fluorescence imaging, mechanical theory, and simulations, we report a fractal wrinkling morphogenesis program that differs radically from the well-known coalescence of wrinkles into folds that occurs in passive thin films at fluid–fluid interfaces. Four stages occur: growth of founding colonies, onset of primary wrinkles, development of secondary curved ridge instabilities, and finally the emergence of a cascade of finer structures with fractal-like scaling in wavelength. The time evolution of pellicle formation depends on the initial heterogeneity of the film microstructure. Changing the starting bacterial seeding density produces three variations in the sequence of morphogenic stages, which we term the bypass, crystalline, and incomplete modes. Despite these global architectural transitions, individual microcolonies remain spatially segregated, and thus, the community maintains spatial and genetic heterogeneity. Our results suggest that the memory of the original microstructure is critical in setting the morphogenic dynamics of a pellicle as an active biomaterial.

细菌细胞可以在流体-流体界面自组织成结构化的群落。这些由细胞和细胞外基质组成的柔软的活材料称为薄膜。存在于薄膜中的细胞获得了群体水平的生存优势，例如增加了抗生素抗性。薄膜形成的动力学，更一般地说，复杂的形态是如何由限制在界面处的活性生物材料产生的，目前尚不清楚。在这里，使用霍乱弧菌作为我们的模型有机体、定制的自适应立体显微镜、荧光成像、力学理论和模拟，我们报告了一种分形皱纹形态发生程序，该程序与众所周知的皱纹合并成褶皱在流体中的被动薄膜中发生根本不同——流体界面。四个阶段发生：创始菌落的生长、初级皱纹的出现、次级弯曲脊不稳定性的发展，最后出现一系列更精细的结构，其波长呈分形状缩放。薄膜形成的时间演变取决于薄膜微结构的初始异质性。改变起始细菌播种密度会在形态发生阶段的序列中产生三种变化，我们称之为旁路、结晶和不完整模式。尽管有这些全球性的建筑转变，个体微菌落在空间上仍然是隔离的，因此，群落保持了空间和遗传的异质性。我们的研究结果表明，原始微结构的记忆对于将薄膜的形态动力学设置为活性生物材料至关重要。