Multiscale Studies of Collective Behavior in a Model Social Bacterium

个体群体形成复杂和动态空间格局的能力是生物现象的一个关键方面，从集体行为到多细胞发展。在细胞环境中，这通常涉及复杂的化学信号和趋化策略。然而，PI最近发现，一些细菌物种已经进化到可以利用活性物质相分离的优势，在不需要化学信号的情况下产生图案。该项目努力从物理学家的角度理解这一过程，但由于缺乏物理探测运动细菌群的机械特性和相互作用的工具而受到阻碍。PI对单细胞细菌黄粘球菌的研究重点是在集体饥饿诱导的子实体形成开始时产生力的分子细节和细胞之间的相互作用。在这个项目中，PI试图将子实体的发育过程解释为一个积极的脱湿过程，将新的理论模型与前沿的实验数据联系起来。PI的研究目标得到了一个扩展计划的补充，该计划旨在让更多的本科生参与生物物理学，并通过公开讲座吸引非科学家参与。PI在未来几年的目标包括(1)为一年级本科生扩展综合科学项目，(2)为高年级本科生开设暑期学校，(3)在纽约市举办一系列公开讲座，旨在通过与日常生活相关的例子来传达生物物理学的兴奋和创新。以下三个目标旨在确定运动性和粘附性在驱动基于饥饿的脱湿中的作用。PI目前的黏液球菌聚集模型依赖于二维的粒子干扰。虽然这些令人难以置信的简单模型捕获了一些观察到的现象，但实际的动态发生在3D中，因为人口从表面脱落而不会阻塞形成圆形液滴。这个更复杂的现实需要更精密的实验数据。该实验室结合了黄粘球菌运动性、尖端成像技术、力显微镜和计算机视觉分析方面的专业知识，使该小组具有开展拟议研究的独特资格。目标1：为了了解细胞在彼此之间和在基质上产生的力，PI将使用定制的光学捕获显微镜和缺乏特定运动蛋白和粘附分子的突变菌株来测量细胞间和细胞-基质的机械相互作用。目标2：为了探测子实体内细胞的运动，该小组将使用共聚焦显微镜在3D中跟踪细胞，以(i)比较聚集体中不同位置随时间的运动，以及（ii）研究子实体内分层结构和流动的形成。目标3：为了探索子实体形成的宏观力学，该小组将(i)使用共聚焦成像和原子力显微镜测量液滴形状和流变性的发展，以及（ii）使用牵引力显微镜探测基材上产生的力。在每一步中，来自三个目标的数据将被用于测试由该小组合作者开发的主动脱湿理论，并被其测试。该项目通过使用物理测量和分析来了解活细胞在空间尺度上的动力学，牢牢地符合美国国家科学基金会生命系统物理学计划的目标。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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 individuals to form complex and dynamic spatial patterns is a key aspect of biological phenomena ranging from collective behavior to multi-cellularity to development. In a cellular context, this often involves complicated chemical signaling and chemotaxis strategies. However, the PI has recently discovered that some bacterial species have evolved to take advantage of an active-matter phase separation that generates patterns without the need for chemical signaling. This project strives to understand this process from a physicist's perspective, but is hindered by a lack of tools to physically probe the mechanical properties and interactions of groups of motile bacteria. The PI's work with the single-celled bacterium Myxococcus xanthus focuses on the molecular details of force generation and the interactions of cells at the start of collective starvation-induced fruiting body formation. In this project, the PI seeks to explain the process of fruiting body development as an active dewetting process, linking new theoretical models with cutting-edge experimental data. The PI's research goals are complemented by an outreach plan that aims to involve more undergraduate students in biological physics and to engage non-scientists through public lectures. The PI's goals over the next few years include (i) expanding the Integrated Science program for first year undergraduates, (ii) starting a summer school aimed at advanced undergraduates, and (iii) putting on a series of public lectures in New York City meant to convey the excitement and innovation of biophysics using examples relevant to everyday life.The three aims below seek to determine the role of motility and adhesion in driving starvation-based dewetting. The PI's current models of Myxococcus xanthus aggregation rely on particle jamming in 2D. While these incredibly simple models capture some of the observed phenomena, the actual dynamics occur in 3D as the population dewets off the surface without jamming to form round droplets. This more complicated reality requires more sophisticated experimental data. The laboratory combines expertise in Myxococcus xanthus motility, cutting-edge imaging techniques, force microscopy, and computer vision analyses, making the group uniquely qualified to carry out the proposed research. Aim 1: To understand the forces that cells generate on each other and on a substrate, the PI will measure cell-cell and cell-substrate mechanical interactions using a custom-built optical trapping microscope and mutant strains that lack specific motor proteins and adhesion molecules. Aim 2: To probe the motility of cells inside a fruiting body, the group will track cells in 3D using confocal microscopy to (i) compare the motion over time and between different locations in the aggregate, and (ii) investigate the formation of layered structures and flows within the fruiting body. Aim 3: To probe the macroscopic mechanics involved in fruiting body formation, the group will (i) measure the development of droplet shape and rheology using confocal imaging and atomic force microscopy, and (ii) probe the forces generated on the substrate using traction force microscopy. At each step, data from the three aims will be used to test, and be tested by, the active-dewetting theories being developed by the group's collaborators. This project lies firmly within the goals of the Physics of Living Systems program at the NSF by using physical measurements and analyses to understand the dynamics of living cells across spatial scales.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.