"The locomotion of microorganisms in fluids is a theme of major importance in biology. It affects many processes such as mammalian reproduction, the marine life ecosystem, and the dynamics of bacterial infection. Locomotion is typically achieved by the periodic deformation of flagella (short and flexible organelles) that drive the fluid motion around the microorganisms, and generate propulsive forces. The shape of the flagella is, in turn, affected by the fluid dynamics forces generated by the organisms. The understanding of this complex fluid-structure interaction calls for a multidisciplinary approach, at the intersection of physics, mechanics, biology and applied mathematics. The present research and training project will be dedicated to some open fundamental issues of flagellar propulsion. One key point of its methodology is the combined experimental and theoretical approach. A macroscopic experiment will be built with the aim of mimicking the motion of a bacterial flagellum. By immersing a rotating flexible filament in a highly viscous fluid, the fluid mechanics is identical to what occurs at the microorganism scale but with the advantages of a perfectly controllable experiment. Several important phenomena will be studied independently such as the motion in a viscoelastic fluid, the interaction of several flagella, the mixing properties of the fluid dynamics, and the effect of intrinsic curvature on the propulsion efficiency. In parallel, theoretical models will be developed with the aim of providing deeper insight into the physical mechanisms by extending the regimes of the actual models (resistive force, and slender-body models). This proposal is related to important Health issues such as bacterial infection, sperm motility and the design of micro-robots able to perform minimally invasive surgery and targeted drug delivery. This project will therefore contribute to European competitiveness on two major themes of the FP7 Programme: Health and Nanosciences."