Simple optical analysis of viability of fission yeast based on electro-orientation with transparent electrodes

Rapid and easy viability assays of microorganisms are important for the efficient control of fermentation processes. A simple optical analysis system for viability assay of cylindrical fission yeast cells was developed to accurately measure the transmittance changes from electro-orientation (EO) of the cells in an alternating current electric field without a microscope. A single incident light beam was directed vertically through the horizontally placed optically transparent indium-tin-oxide plate electrodes. Transmittance was enhanced distinctly when cells oriented from perpendicular (elongated shape) to parallel (circular shape) to the direction of the light beam due to a decrease in the projected area of the cell shape. Transmittance of each living and dead cell suspension was different with respect to the frequency. Survival rate was readily estimated by measuring three transmittance (T) values at specific frequencies. Initial T₀ was obtained without the application of an electric field, as all cells were elongated in shape. Maximum T₁ was achieved at 500 kHz, as all cells were circular in shape. T₂ was changed between T₀ and T₁ at 10 MHz, which was dependent on the circular shape of the living cells. This EO-optical method offers a rapid and easy process for viability assessment of non-spherical cells without a calibration curve.