Mechanics of Bacterial Swarming

描述（由申请方提供）：群集是一种特殊形式的细菌运动性，当可以游动的细胞在潮湿琼脂表面的丰富培养基中生长时，会产生群集。细胞变成多核的，伸长的，合成大量的鞭毛，分泌湿润剂，并在协调的包装中穿过表面。大多数关于群集的研究都试图定义从植物状态到群集状态的发育过程。这些研究提出了为什么细胞会成群的问题。我们的目标是了解细胞是如何聚集的。要回答的问题不仅与表面附近的基本鞭毛力学有关，而且与该过程的更大分支有关，例如在表面定殖期间细胞的群体行为，包括图案生成和生物膜形成。如果能够充分了解细胞的作用，那么就有可能准确地模拟这一过程，甚至可能通过新的手段对其进行干扰。这项工作将在大肠杆菌中进行，大肠杆菌是最了解运动性的生物体。1)使用单一和多色荧光标记的鞭毛细丝与脉冲激光照明相衬成像，数字视频记录，和逐帧的计算机分析，我们将表征运动的细胞和它们的鞭毛附近的领先优势的群。鞭毛在拥挤的群体环境中的运动与细胞在稀介质中的运动有何不同？鞭毛在协调行为中扮演什么角色？2)通过跟踪相衬图像，我们将测量相关的距离和时间的细胞在不同区域的群体。协调运动的范围是多少？3)蜂群边界是如何扩展的？如果我们能找到合适的标记，我们将尝试了解流体如何在群的前沿移动。液体是由鞭毛运动还是由底层琼脂的渗透流向外驱动的？我们希望，通过澄清群体细胞的行为，其他研究人员将有一个更基本的理解，以指导调查更复杂的方面的表面殖民，包括入侵性和致病性。公共卫生相关性：我们正试图了解鞭毛细菌如何在潮湿的表面上移动，即，细菌群集的机制这种运动使细胞能够侵入并定殖人体组织或医疗器械，因此是发病机制中的重要因素。

DESCRIPTION (provided by applicant): Swarming is a specialized form of bacterial motility that develops when cells that can swim are grown in a rich medium on the surface of moist agar. The cells become multinucleate, elongate, synthesize large numbers of flagella, excrete wetting agents, 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. Such studies ask why cells swarm. Our aim is to understand how cells swarm. The questions to be answered are pertinent not only to basic flagellar mechanics near 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. If enough can be learned about what cells do, then it should be possible to accurately model the process and perhaps even interfere with it by novel means. The work will be done with Escherichia coli, the organism for which motility is best understood. 1) Using single and multi-color fluorescent labeling of flagellar filaments with pulsed laser illumination together with phase- contrast imaging, digital video recording, and frame-by-frame computer analysis, we will characterize the motion of cells and of their flagella near the leading edge of the swarm. How does the motion of flagella in the crowded environment of a swarm differ from that of cells swimming in dilute media? What roles do flagella play in coordinated behavior? 2) By tracking phase-contrast images, we will measure correlation distances and times of cells in different regions of the swarm. What is the range of coordinated motion? 3) How does the swarm boundary expand? If we can find suitable markers, we will try to learn how fluid moves in front of the leading edge of the swarm. Is fluid driven outward by flagellar motion or by osmotic flow from the underlying agar? It is our hope that by clarifying the behavior of the swarm cell, other researchers will have a more fundamental understanding to guide investigations on more complicated aspects of surface colonization, including invasiveness and pathogenicity. PUBLIC HEALTH RELEVANCE: We are trying to understand how flagellated bacteria move over moist surfaces, i.e., the mechanics of bacterial swarming. This motion enables cells to invade and colonize human tissue or medical devices, and thus is an important factor in pathogenesis.