Mechanics of Bacterial Swarming

描述（由申请人提供）：群集是细菌运动的一种特殊形式，当能够游泳的细胞在潮湿琼脂表面的丰富培养基中生长时，就会发展起来。细胞变得多核，伸长，合成大量鞭毛，分泌湿润剂，并以协调的群体在表面上移动。大多数关于蜂群的研究都试图定义从植物状态到蜂群状态的发育过程。这类研究询问细胞聚集的原因。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，例如细胞在表面定植期间的群体行为，包括模式生成和生物膜形成。如果对细胞的功能有足够的了解，那么就有可能精确地模拟这一过程，甚至可能用新的方法来干预这一过程。这项工作将在大肠杆菌中进行，这种生物的运动性是最容易理解的。1)利用脉冲激光照射下鞭毛细丝的单色和多色荧光标记，结合相衬成像、数字视频记录和逐帧计算机分析，我们将描绘细胞及其鞭毛在群体前沿附近的运动特征。鞭毛在群体拥挤环境中的运动与细胞在稀释介质中的运动有何不同？鞭毛在协调行为中起什么作用？2)通过跟踪相衬图像，我们将测量群体中不同区域细胞的相关距离和次数。协调运动的范围是什么？3)蜂群边界如何扩展？如果我们能找到合适的标记，我们将尝试了解在蜂群前沿前的流体是如何移动的。液体是由鞭毛运动引起的还是由底层琼脂的渗透流动引起的？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了解，以指导研究更复杂的表面定植方面，包括侵袭性和致病性。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，即细菌群的机制。这种运动使细胞能够侵入和定植人体组织或医疗设备，因此是发病的一个重要因素。

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.