THE ROLE OF HYDRODYNAMIC INTERACTION IN THE LOCOMOTION OF MICROORGANISMS

A general Boundary Element Method is presented and benchmarked with ex isting Slender Body Theory results and reflection solutions for the mo tion of spheres and slender bodies near plane boundaries. This method is used to model the swimming of a microorganism with a spherical cell body, propelled by a single rotating flagellum. The swimming of such an organism near a plane boundary, midway between two plane boundaries or in the vicinity of another similar organism, is investigated. It i s found that only a small increase (less than 10%) results in the mean swimming speed of an organism swimming near and parallel to another i dentical organism. Similarly, only a minor propulsive advantage (again , less than 10% increase in mean swimming speed) is predicted when an organism swims very close and parallel to plane boundaries (such as a microscopic plate and (or) a coverslip, for example). This is explaine d in terms of the flagellar propulsive advantage derived from an incre ase in the ratio of the normal to tangential resistance coefficients o f a slender body being offset by the apparently equally significant in crease in the cell body drag. For an organism swimming normal to and t oward a plane boundary, however, it is predicted that (assuming it is rotating its flagellum, relative to its cell body, with a constant ang ular frequency) the resulting swimming speed decreases asymptotically as the organism approaches the boundary.