Single-Cell Motility Analysis of Stimulated Diatoms using a Microchamber

Abstract

Motility of diatom cells that were stimulated by irradiation with controlled visible lights were studied using a microchamber. Isolated Navicula sp. cells were deposited in a microchamber made of poly(dimethylsiloxane) in order to realize a long period observation. In the first experiment, the diatom cells were continuously observed for 60 min by an optical microscope. If the microchamber does not appropriately work, the 60 min observation should be difficult, because the cells were moved outside the observation area. In the first 20 min, the cells were irradiated by a halogen lamp. Then, the light shielded by a cut-off filter (cut-off wavelength: 550 nm) irradiated to the sample for the next 20 min. In the final 20 min, the sample was irradiated without the filter again. Brightness was kept at 500 lux for 60 min by a dimming filter to avoid effects of brightness. Then, movements of 17 individual cells were analyzed by a two-dimensional trajectory analysis software. As a result, the velocities of 12 cells were decreased while the light was shielded by the filter (20-40 min). T-test results also suggested that the velocity was significantly decreased. In the second experiments, we prepared small colonies of diatom cells in a microchamber with 12 days incubation. Then, the colonies were irradiated with a mercury lamp with three different cut filters for 100 sec period. In this experiment, we focused on inactive (stopped) cells. The cells were found to start to move after the irradiation. However, after stopping the irradiation, the velocities of the activated cells were decreased gradually. In addition, the decrease was affected by the types of the filters. Our data revealed a possibility of detailed analysis of diatom motility using the microchamber system.