Probes for fluids in bacterial swarms

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表面（如琼脂）的丰富培养基中生长时，会发展成群集。细胞变成多核，伸长，合成大量鞭毛，并在表面形成一层薄薄的液体。通过提供细胞游动和相互作用的微环境，这种液体在蜂群生理学中起着重要作用。蜂群促进传染性病原体的侵袭，因此在医学上是相关的。对于我们研究的模式生物大肠杆菌，细胞实际上是在两个固定表面之间的一层液体薄膜中游动，上面是表面活性剂单层（固定在边缘），下面是琼脂。在蜂群的前面，由附着在蜂群边缘附近的琼脂上的细胞的鞭毛运动驱动的流体顺时针流动（从上面看蜂群）。在蜂群体内，流体向内和向外漂移，流向距离蜂群边缘约100米的区域。这是细胞生长迅速和表面细胞密度高的区域。为了使细胞生长和蜂群扩大，必须从下面的琼脂中提取液体。一个长期存在但未经证实的假设是，蜂群流体是通过渗透流动从基质中抽取出来的。我们建议通过测量靠近群体边缘的群体流体渗透压变化的时空动态来检验这一假设。我们将测量填充自猝灭和非自猝灭染料（后者作为对照）的脂质体的大小变化，在含有胶体二氧化硅的介质中添加，以防止脂质体下沉和被琼脂捕获。该项目专注于群体动力学的一个主要未解决的核心问题，但涉及的方法也可以应用于实时测量涉及群体细胞分化的其他重要生理参数。我们还将尝试开发用于粘度和pH的浮力颗粒探针。

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.