Jena Pratikshya, Mishra Shradha
Department of Physics, Indian Institute of Technology (BHU), Varanasi, 221005, India.
Sci Rep. 2025 Aug 22;15(1):30948. doi: 10.1038/s41598-025-13297-5.
We present a theoretical model to explore the dynamics and phase evolution of growing bacterial suspensions. The model described by the hydrodynamic evolution of bacterial density, orientation, and fluid velocity, incorporating birth and death terms to account for colony growth. Starting from a low-density regime, the system undergoes structural and dynamical transitions driven by bacterial proliferation, leading to the emergence of distinct phases: dilute, turbulent, and heterogenous. At low density, bacteria show local ordering, which transitions to clustering and eventually to a turbulent phase with spatiotemporal vortices of varying scales, as observed in dense suspensions. As density increases, orientation becomes increasingly inhomogeneous and random, indicating heterogeneity. Our findings emphasize the critical role of growth in emergence of phases, illustrating how a single system can sequentially transit through different phases over time. We provide a comprehensive understanding of the evolving patterns and behaviors within growing bacterial colonies, which makes our work different from previous studies on dense bacterial suspensions. Since the growth is generic to active system hence the current work bridges theory and experiment, offering insights into the self-organization and emergent phases in active matter systems driven by growth.
我们提出了一个理论模型来探索生长中的细菌悬浮液的动力学和相演化。该模型由细菌密度、取向和流体速度的流体动力学演化描述，并纳入了出生和死亡项以解释菌落生长。从低密度状态开始，系统在细菌增殖的驱动下经历结构和动力学转变，导致出现不同的相：稀释相、湍流相和异质相。在低密度时，细菌表现出局部有序，随着密度增加，这种有序转变为聚集，最终转变为具有不同尺度时空涡旋的湍流相，这在高密度悬浮液中也有观察到。随着密度的增加，取向变得越来越不均匀和随机，表明存在异质性。我们的研究结果强调了生长在相出现中的关键作用，说明了一个单一系统如何随着时间依次经历不同的相。我们对生长中的细菌菌落内不断演变的模式和行为提供了全面理解，这使我们的工作有别于以往对高密度细菌悬浮液的研究。由于生长是活性系统的普遍特征因此当前工作架起了理论与实验之间的桥梁，为受生长驱动的活性物质系统中的自组织和涌现相提供了见解。
