Active Matter Phases and Phase Transitions in a Model Social Bacterium

个体有机体群体形成复杂和动态空间模式的能力是从鸟群和鱼群到多细胞和胚胎发育等生物现象的一个关键方面。在细菌种群中，这通常涉及细胞之间复杂的信号机制。然而，一些物种已经进化到利用一种被称为活性物质的特殊物理学来执行特定的生物功能，而不需要细胞之间的化学信号。在社会细菌黄色粘球菌中，Shaevitz小组已经证明细胞可以形成类似鸟群、蚂蚁踪迹和液滴的多细胞群。这些细胞可以根据环境线索改变它们的移动方式，从而改变种群的行为。这个项目展示了一系列的实验和理论分析，以从物理学家的角度来理解这些过程，使用工具来测量这些群体中的空间方向、流动和力。这项工作的结果将回答有关黄曲霉集体行为的机制和功能的基本问题，并有助于我们理解有机体群体如何集体行动。在未来，这可能会导致开发利用主动物理原理自组装的微米和纳米技术的新方法。该项目专注于三个问题：饥饿期间三维液滴是如何形成的，表面波不稳定如何帮助捕食行为，以及这些行为如何在类似自然土壤的环境中表现出来。为了了解3D子实体是如何从2D湿润的层中出现的，研究人员将跟踪整个种群在发育过程中的向列相顺序、细胞运动和机械应力。为了了解在捕食过程中控制涟漪行为的不稳定性，研究人员将测量种群的高度，并跟踪细胞运动，同时扰乱运动、细胞之间的相互作用和环境。为了在更真实的基质上探索黄花莲的相变，研究人员将测量弯曲基质和水化土壤人工胶体模型上的运动性、子实体形成和涟漪。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The ability of groups of individual organisms to form complex and dynamic spatial patterns is a key aspect of biological phenomena ranging from bird flocking and fish schooling to multicellularity and embryonic development. In bacterial populations, this often involves complicated signaling mechanisms between cells. However, some species have evolved to take advantage of a special kind of physics called active matter to perform specific biological functions without the need for chemical signaling between cells. In the social bacterium Myxococcus xanthus, the Shaevitz group have shown that cells can form multicellular groups that resemble bird flocks, ant trails, and liquid droplets. These cells can change the way they move in response to environmental cues to change the behavior of the population. This project lays out a series of experiments and theoretical analyses to understand these processes from a physicist’s perspective, using tools to measure the spatial orientations, flows, and forces in these populations. Results from this work will answer fundamental questions about the mechanism and function of M. xanthus collective behavior and inform our understanding of how groups of organisms act collectively. In the future, this may lead to new methods for developing micro- and nanotechnologies that self-assemble using the principles of active physics.This project focuses on three questions: how three-dimensional droplets form during starvation, how a surface-wave instability aids predatory behavior, and how these behaviors manifest in naturalistic soil-like environments. To understand how 3D fruiting bodies emerge from 2D wetted layers, the investigators will track nematic order, cell motion, and mechanical stress throughout the population during development. To understand the instability that governs rippling behavior during predation, the investigators will measure the height of the population and track cell motion while perturbing motility, interactions between cells, and the environment. To probe M. xanthus phase transitions on more realistic substrates, the investigators will measure motility, fruiting body formation, and rippling on curved substrates and artificial colloidal models of hydrated soils.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.