US-UK Cooperative Science: Stochastic and Deterministic Components of Micro-organism Trajectories

该奖项将支持亚利桑那大学的John Kessler博士和英国利兹大学应用数学系的T.J. Pedley教授之间的合作研究。该项目的目的是研究非肌肉细胞中肌动球蛋白为基础的细胞运动的分子基础。研究人员将重点关注游泳生物的个体和集体动力学，特别是藻类细胞。它们游动路径的几何形状是由重力和剪切作用的扭矩决定的，这些扭矩决定了生物身体的方向。细胞也对光照的方向和强度以及随机脉冲作出反应。耦合方向与剪切力矩和重力力矩的物理参数还不准确。从理论中得出的数量级足以模拟大量微型游泳者的合作行为，但没有对单个细胞轨迹的直接测量。此外，对感觉定向及其与物理定向机制的数量竞争基本上一无所知。这个项目的主要目的是开发一种仪器，从设计到原型，用于测量细胞方向对剪切速率、重力方向和光照的依赖。该装置将用于提供定量的实验值，以插入描述个体游泳轨迹的方程，以及作为游泳生物集体相互作用的结果而发展的模式。这项合作将受益于凯斯勒博士在物理学和活动藻类生态学方面的互补专业知识，以及佩德利博士在应用数学和生理流动方面的互补专业知识。这项研究的结果将在活性悬浮液理论、微生物生态学和细胞感觉反应的量化中得到应用。

This award will support collaborative research between Dr. John Kessler, University of Arizona and Professor T.J. Pedley, Department of Applied Mathematics, University of Leeds, England. The objective of the proposed project is an investigation of the molecular basis of actomyosin-based cell motility in non-muscle cells. The investigators will focus on individual and collective dynamics of swimming organisms, especially algal cells. The geometry of their swimming paths is due to torque exerted by gravity and shear, which orient the organisms' bodies. Cells also respond to the direction and intensity of illumination and to random impulses. The physical parameters which couple orientation to shear and gravity torques are not accurately known. Magnitudes derived from theory are adequate to model the cooperative behavior of large populations of micro-swimmers, but there are no direct measurements on individual cell trajectories. Furthermore, essentially nothing is known about sensory orientation and its quantitative competition with physical orienting mechanisms. The chief object of this project is to develop an apparatus, from design to prototype, for measuring the dependence of cell orientation on shear rate on the direction of gravity, and of illumination. This apparatus will be used to provide quantitative experimental values for insertion in the equations which describe individual swimming trajectories and also the patterns which develop as a result of the collective interactions of swimming organisms. This cooperative effort will benefit from the complementary expertise of Dr. Kessler in physics and the ecology of motile algae, and of Dr. Pedley in applied mathematics and physiological flows. The results of this research will find application in the theory of active suspensions, in microbial ecology, and in the quantification of cellular sensory responses.