Development of a whole-cell-based screening method for a carotenoid assay using aerial microalgae

Non-destructive approaches based on the application of optical spectroscopy are important for monitoring carotenoid accumulation in a whole cell cultured under various conditions. A simple and rapid assay utilizing aerial microalgae helps to identify stress conditions that can efficiently enhance the carotenogenesis in photosynthetic organisms. The spectra of cell suspensions were characterized in the aerial microalga Coelastrella sp. KGU-Y002, which are unicellular and undifferentiated. Total carotenoid contents could be successfully estimated on the basis of the absorbance values of the cell suspensions and calibration data analyzed by HPLC (high-performance liquid chromatography). A novel screening method, the so-called “whole-cell-based screening method” for carotenoid assays (WCA), was developed based on this procedure. It was possible to investigate the effects of various stresses on carotenoid accumulation in the aerial microalga by adapting this bioassay to a 96-well microtiter plate. When bioactive compounds were screened from our library of plant extracts using this method, an active compound was identified from the plant extract.