Single cell analysis of sinking diatoms studied using a homemade 'tumbled' optical microscope system

Diatoms are one of the major photosynthetic planktons. Here, we studied movements of aqueous suspensions of diatoms using a home-made 'tumbled' optical microscope system. The usual inverted optical microscope was reoriented using a homemade microscope stand so that the vertical sample stage contacted the surface. To observe the intrinsic sinking phenomenon of individual Navicula sp. cells, which have slender bodies, a homemade microchamber (1 mm³) was employed. Most of the cells uniformly sunk with a velocity of 2 to 14 μm/s. Automatic and manual two points trajectory analyses were carried out. The manual analysis was able to assess the rotation of cells. The novel methods provide new information about cell movements in aqueous systems that could not be obtained using conventional methods.