Effects of cell length on the swimming behavior of flagellated bacteria near a solid surface

It is well known that flagellated bacteria swim in circular trajectories near surfaces due to increased hydrodynamic drag on the counter-rotating flagella and cell body. Little work, however, has been done to investigate the effects of cell length on these circular trajectories. We perform such a study on a gut bacterium, Enterobacter sp. SM3, which is peritrichous and rodlike, but can grow to variable length. We found that the strong boundary surface not only causes the run trajectories to become circular, but it also restricts the tumbles into brief turns after which the bacterium continues to swim in circular trajectories close to the surface. Measuring the motion of hundreds of cells near the glass surface, we found that the average linear speed, angular speed, and curvature all depend weakly on the cell length. These results are compared with computer simulations that take into account the cell size and near-surface hydrodynamic interactions.