The effect of long-range hydrodynamic interaction on the swimming of a single bacterium.

It has been theoretically suggested that when a bacterium swims in a fluid, the disturbance it creates is long-ranged and can influence its locomotion. The contribution of these long-range hydrodynamic interactions to swimming cells is examined herein for a number of bacterial strains with well-defined flagellar geometries. We show experimentally for the first time that long-range hydrodynamic interactions are important for an accurate description of the swimming of a single cell, and the effect is more pronounced for bacteria with a large cell body. The commonly used local resistive force theory assumes a stationary background fluid while ignoring flows induced due to other moving parts of the cell. Although pedagogically attractive, resistive force theory is not generally applicable to experiment.