Probes for fluids in bacterial swarms

描述(申请人提供)：群聚是一种特殊的细菌运动形式，当会游泳的细胞在潮湿表面的丰富介质中生长时，例如琼脂。细胞变得多核，延长，合成大量的鞭毛，并在一层薄薄的液体中穿过表面。这种液体通过提供细胞可以游泳和相互作用的微环境，在蜂群的生理学中发挥着重要作用。蜂群增加了传染性病原体的侵袭性，因此与医学有关。对于我们研究的模式生物大肠杆菌，细胞实际上在两个固定表面之间的一层薄薄的液体中游泳，上面是表面活性剂单分子层(固定在其边缘)，下面是琼脂。在蜂群的前面，液体顺时针方向流动(从上方看蜂群)，这是由于附着在靠近蜂群边缘的琼脂上的细胞鞭毛的运动所驱动的。在蜂群体内，液体向内和向外漂移，流向距离蜂群边缘约100？m的区域。这是一个细胞生长迅速、表面细胞密度高的区域。为了让细胞生长和蜂群扩张，必须从下面的琼脂中提取液体。一个长期存在但未经检验的假设是，菌群液体是通过渗透流动从底物中吸取的。我们建议通过测量群体边缘附近群体流体渗透压变化的时空动力学来检验这一假说。我们将测量在含有胶体二氧化硅的介质中填充自猝灭和非自猝灭染料(后者作为对照)的脂质体的尺寸变化，添加胶体二氧化硅是为了防止脂质体下沉和被琼脂包裹。该项目关注的是群体动力学中一个尚未回答的主要问题，但涉及的方法也可以应用于实时测量与群体细胞分化有关的其他重要生理参数。我们还将尝试开发用于测量粘度和pH值的浮力微粒探头。

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 a moist surface, e.g., agar. The cells become multinucleate, elongate, synthesize large numbers of flagella, and advance across the surface in a thin layer of fluid. The fluid plays a significant role in the physiology of swarming by providing the microenvironment in which cells can swim and interact. Swarming promotes invasiveness of infectious pathogens and thus is medically relevant. With E. coli, the model organism that we study, the cells actually swim in a thin film of fluid between two fixed surfaces, a surfactant monolayer above (pinned at its edges) and agar below. Ahead of the swarm, fluid streams clockwise (with the swarm viewed from above) driven by the motion of flagella of cells stuck to the agar near the swarm edge. Within the body of the swarm, fluid drifts both inwards and outwards toward a region about 100 ¿m from the swarm edge. This is a region of rapid cell growth and high surface cell density. For cells to grow and the swarm to expand, fluid must be extracted from the underlying agar. A long-standing but untested hypothesis is that the swarm fluid is drawn from the substrate by osmotic flow. We propose to test this hypothesis by measuring the spatial-temporal dynamics of changes in osmolarity in the swarm fluid near the swarm edge. We will measure changes in the size of liposomes filled with self-quenching and non-self- quenching dyes (the latter as a control) in a medium containing colloidal silica, added to prevent liposomes from sinking and being entrapped by the agar. This project is focused on a major unanswered question central to swarm dynamics, but involves methods that can be applied, as well, to real-time measurements of other important physiological parameters involved in swarm-cell differentiation. We also will try to develop buoyant particulate probes for viscosity and pH.