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

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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.