Lama Hisay, Yamamoto Masahiro J, Furuta Yujiro, Shimaya Takuro, Takeuchi Kazumasa A
Department of Physics, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
National Metrology Institute of Japan, National Institute of Advanced Industrial Science and Technology, 1-1-1 Umezono, Tsukuba 305-8560, Japan.
PNAS Nexus. 2024 Jun 14;3(7):pgae238. doi: 10.1093/pnasnexus/pgae238. eCollection 2024 Jul.
Densely packed, motile bacteria can adopt collective states not seen in conventional, passive materials. These states remain in many ways mysterious, and their physical characterization can aid our understanding of natural bacterial colonies and biofilms as well as materials in general. Here, we overcome challenges associated with generating uniformly growing, large, quasi-two-dimensional bacterial assemblies by a membrane-based microfluidic device and report the emergence of glassy states in two-dimensional suspension of . As the number density increases by cell growth, populations of motile bacteria transition to a glassy state, where cells are packed and unable to move. This takes place in two steps, the first one suppressing only the orientational modes and the second one vitrifying the motion completely. Characterizing each phase through statistical analyses and investigations of individual motion of bacteria, we find not only characteristic features of glass such as rapid slowdown, dynamic heterogeneity, and cage effects, but also a few properties distinguished from those of thermal glass. These distinctive properties include the spontaneous formation of micro-domains of aligned cells with collective motion, the appearance of an unusual signal in the dynamic susceptibility, and the dynamic slowdown with a density dependence generally forbidden for thermal systems. Our results are expected to capture general characteristics of such active rod glass, which may serve as a physical mechanism underlying dense bacterial aggregates.
紧密堆积、具有运动能力的细菌能够呈现出传统被动材料中未见的集体状态。这些状态在许多方面仍然神秘莫测，对其进行物理表征有助于我们理解天然细菌菌落和生物膜，以及一般意义上的材料。在这里，我们通过一种基于膜的微流控装置克服了与生成均匀生长、大型准二维细菌聚集体相关的挑战，并报告了在……的二维悬浮液中出现玻璃态。随着细胞生长导致数量密度增加，运动细菌群体转变为玻璃态，此时细胞紧密堆积且无法移动。这分两步进行，第一步仅抑制取向模式，第二步使运动完全玻璃化。通过对细菌个体运动的统计分析和研究来表征每个相，我们不仅发现了玻璃的特征，如快速减速、动态异质性和笼效应，还发现了一些与热玻璃不同的特性。这些独特的特性包括具有集体运动的排列细胞微域的自发形成、动态磁化率中出现异常信号，以及热系统通常禁止的与密度相关的动态减速。我们的结果有望捕捉到这种活性棒状玻璃的一般特征，这可能是密集细菌聚集体背后的物理机制。
