Mechanics of Bacterial Swarming

描述(申请人提供)：菌群是一种特殊的细菌运动形式，当在肉汤中游泳的细胞在潮湿的琼脂表面的丰富介质中生长时形成。它们变成多核的，拉长，合成大量的鞭毛，分泌表面活性物质，并以协调的方式穿过表面。大多数关于蜂群的研究试图定义从营养状态到蜂群状态的发育过程，并发现蜂群在侵袭性和致病性中所起的作用。在这里，我们将看看鞭毛在蜂群中到底做了什么，它们如何决定细胞群的协调运动，并促进蜂群边界的流体流动。这些问题不仅与表面上的基本鞭毛机制有关，而且与这一过程的更大分支有关，例如细胞在表面定植期间的群体行为，包括图案生成和生物膜的形成。1)利用鞭毛细丝的单色和多色荧光标记、脉冲激光照射、数字录像和逐帧计算机分析，我们将表征鞭毛在蜂群前沿的细胞上和在靠近边缘的成群移动的细胞上的运动。我们将对群体缺陷趋化性(CHE)突变体和这些突变体的回复突变体重复这些测量。蜂群运动的鞭毛机制是什么？2)通过跟踪荧光细胞，我们将测量蜂群不同区域，特别是靠近其前沿的细胞的相关距离和时间。这些运动的协调性如何？3)通过跟踪小的荧光珠，我们将研究蜂群前沿的流体运动。流体是由鞭毛运动向外驱动的吗？4)为了更多地了解表面活性剂所起的作用，我们将测量在菌群前缘附近采样的流体的界面张力。表面活性物质的产生是否与鞭毛的运动有关？简而言之，我们希望了解使鞭毛细菌能够在表面定植的潜在机械机制，这是一个对多细胞、侵袭性和致病性很重要的过程。

DESCRIPTION (provided by applicant): Swarming is a specialized form of bacterial motility that develops when cells that swim in broth are grown in a rich medium on the surface of moist agar. They become multinucleate, elongate, synthesize large numbers of flagella, excrete surfactants, and advance across the surface in coordinated packs. Most studies of swarming have sought to define the developmental processes leading from the vegetative to the swarming state and to discover the role played by swarming in invasiveness and pathogenicity. Here, we will look to see what the flagella actually do in swarming, how they determine the coordinate motion of groups of cells and promote fluid flow at the swarm boundary. These questions are pertinent not only to basic flagellar mechanics on a surface, but also to larger ramifications of this process, such as the group behavior of cells during surface colonization, including pattern generation and biofilm formation. 1) Using single and multi-color fluorescent labeling of flagellar filaments, pulsed laser illumination, digital video recording, and frame-by-frame computer analysis, we will characterize the motion of flagella on cells at the leading edge of the swarm and on cells moving in packs near that edge. We will repeat these measurements with swarm-defective chemotaxis (che) mutants and revertants of these mutants. What is the flagellar mechanics of swarming motility? 2) By tracking fluorescent cells, we will measure correlation distances and times of cells in different regions of the swarm, in particular, near its leading edge. How coordinated are these motions? 3) By tracking small fluorescent beads, we will study fluid motion at the leading edge of the swarm. Is fluid driven outward by flagellar motion? 4) To learn more about the role played by surfactants, we will measure the interfacial tension of fluid sampled near the leading edge of a swarm. Is production of surfactant coupled to flagellar motion? In brief, we hope to understand the underlying mechanical mechanisms that enable flagellated bacteria to colonize surfaces, a process important for multicellularity, invasiveness, and pathogenicity.