Three-dimensional swimming motility of microorganism in the near-wall region

Microbial organisms are easily observed in geometrically confined environments. The swimming characteristics of these microorganisms are largely influenced by the presence of a solid surface. Their swimming behavior in the near-wall region shows different physical motilities. In this study, digital in-line holographic particle tracking velocimetry technique is used to investigate the three-dimensional (3D) motile characteristics of Prorocentrum minimum, especially in the near-wall region. The effects of the interaction between the microorganism and a solid wall on the 3D swimming characteristics, such as helix parameters, orientation, and attraction to the wall, are experimentally analyzed. As a result, swimming microorganisms are observed to have high motility and thrust generation near the wall, compared with the unrestrained free-swimming ones. In addition, the swimming direction tends to become parallel to the wall and they concentrate near the solid surface.