Surface Topography Hinders Bacterial Surface Motility

We demonstrate that the surface motility of the bacterium, Pseudomonas aeruginosa, is hindered by a crystalline hemispherical topography with wavelength in the range of 2-8 mu m. The motility was determined by the analysis of time-lapse microscopy images of cells in a flowing growth medium maintained at 37 degrees C. The net displacement of bacteria over 5 min is much lower on surfaces containing 2-8 mu m hemispheres than on flat topography, but displacement on the 1 mu m hemispheres is not lower. That is, there is a threshold between 1 and 2 mu m for response to the topography. Cells on the 4 mu m hemispheres were more likely to travel parallel to the local crystal axis than in other directions. Cells on the 8 mu m topography were less likely to travel across the crowns of the hemispheres and were also more likely to make 30 degrees-50 degrees turns than on flat surfaces. These results show that surface topography can act as a significant barrier to surface motility and may therefore hinder surface exploration by bacteria. Because surface exploration can be a part of the process whereby bacteria form colonies and seek nutrients, these results help to elucidate the mechanism by which surface topography hinders biofilm formation.