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. ? ?
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