近日，美国耶鲁大学的Jing Yan及其研究小组与宾夕法尼亚州立大学的Sulin Zhang以及麻省理工学院的Tal Cohen等人合作并取得一项新进展。经过不懈努力，他们发现生物膜可以作为自成形生长向列相。相关研究成果已于2023年10月9日在国际知名学术期刊《自然—物理学》上发表。
该团队以被水凝胶限制的细菌生物膜为模型系统，展示了三维活性向列相如何通过生长诱导的应力主动调节自身及其边界，进而调节其内部结构。研究发现，随着环境刚度或细胞-基质摩擦的变化，生物膜的形状会发生从穹顶到透镜的急剧转变，这可以通过考虑约束力和界面力之间竞争的理论模型来解释。生长模式决定了边界的进展，进而决定了细胞谱系的轨迹和空间分布。研究人员进一步证明，不断变化的边界和相应的应力各向异性决定了细胞的取向顺序和生物膜内部拓扑缺陷的出现。这一发现可能为开发具有新兴材料特性的程序化微生物群落提供策略。
据悉，活性向列是被动液晶的非平衡模拟，由消耗自由能来驱动突现行为的各向异性单元组成。与显示器中的液晶分子相似，活性向列线中的有序和动力学对边界条件非常敏感。然而，与被动液晶不同的是，活性向列线具有调节其边界的潜力，能够通过自产生应力来实现。
附：英文原文
Title: Biofilms as self-shaping growing nematics
Author: Nijjer, Japinder, Li, Changhao, Kothari, Mrityunjay, Henzel, Thomas, Zhang, Qiuting, Tai, Jung-Shen B., Zhou, Shuang, Cohen, Tal, Zhang, Sulin, Yan, Jing
Issue&Volume: 2023-10-09
Abstract: Active nematics are the non-equilibrium analogue of passive liquid crystals. They consist of anisotropic units that consume free energy to drive emergent behaviour. As with liquid crystal molecules in displays, ordering and dynamics in active nematics are sensitive to boundary conditions. However, unlike passive liquid crystals, active nematics have the potential to regulate their boundaries through self-generated stresses. Here we show how a three-dimensional, living nematic can actively shape itself and its boundary to regulate its internal architecture through growth-induced stresses, using bacterial biofilms confined by a hydrogel as a model system. We show that biofilms exhibit a sharp transition in shape from domes to lenses in response to changing environmental stiffness or cell–substrate friction, which is explained by a theoretical model that considers the competition between confinement and interfacial forces. The growth mode defines the progression of the boundary, which in turn determines the trajectories and spatial distribution of cell lineages. We further demonstrate that the evolving boundary and corresponding stress anisotropy define the orientational ordering of cells and the emergence of topological defects in the biofilm interior. Our findings may provide strategies for the development of programmed microbial consortia with emergent material properties.
DOI: 10.1038/s41567-023-02221-1
Source: https://www.nature.com/articles/s41567-023-02221-1