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，当可以游动的细胞在潮湿表面上的丰富培养基中生长时，琼脂。细胞变成多核，伸长，合成大量鞭毛，并在一层薄薄的液体中穿过表面。液体通过提供细胞可以游泳和相互作用的微环境在群集的生理学中起着重要作用。群集促进传染性病原体的侵袭性，因此具有医学相关性。用大肠在我们研究的模式生物大肠杆菌中，细胞实际上在两个固定表面之间的液体薄膜中游动，表面活性剂单层在上面（固定在其边缘），琼脂在下面。在菌群的前方，由粘附在靠近菌群边缘的琼脂上的细胞鞭毛的运动驱动，流体顺时针流动（从上方观察菌群）。在群体的身体内，流体向内和向外漂移到距离群体边缘约100米的区域。这是一个快速细胞生长和高表面细胞密度的区域。为了使细胞生长和群体扩大，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，蜂群流体是通过渗透流从基质中抽取的。我们建议通过测量群边缘附近的群液渗透压变化的时空动态来验证这一假设。我们将在含有胶体二氧化硅的培养基中测量填充有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，加入胶体二氧化硅是为了防止脂质体下沉并被琼脂截留。该项目的重点是一个主要的悬而未决的问题，中央群集动力学，但涉及的方法，可以应用，以及，实时测量的其他重要的生理参数参与群集细胞分化。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.