THE SWIMMING OF UNIPOLAR CELLS OF SPIRILLUM VOLUTANS - THEORY AND OBSERVATIONS

Bright-field high-speed cinemicrography was employed to record the swi mming of six unipolar cells of Spirillum volutans. A complete set of g eometrical parameters for each of these six cells, which are of typica l but varying dimensions, was measured experimentally. For each cell, the mean swimming linear and angular speeds were measured for a period representing an exact number of flagellar cycles (at least four and u p to 12 cycles). Two independent sets of measurements were carried out for each cell, one relating to the trailing and the other to the lead ing configuration of the flagellar bundle. The geometry of these cells was numerically modelled with curved isoparametric boundary elements (from the measured geometrical parameters), and an existing boundary e lement method (BEM) program was applied to predict the mean swimming l inear and angular speeds. A direct comparison between the experimental ly observed swimming speeds and those of the BEM predictions is made. For a typical cell, a direct comparison of the swimming trajectory, in each of the trailing and the leading flagellar configurations, was al so included. Previous resistive force theory (RFT) as well as slender body theory (SBT) models are both restricted to somewhat non-realistic 'slender body' geometries, and they both fail to consider swimming ki nematics. The present BEM model, however, is applicable to organisms w ith arbitrary geometry and correctly accounts for swimming kinematics; hence, it agrees better with experimental observations than do the pr evious models.