Composition of carotenoids and identification of aerial microalgae isolated from the surface of rocks in mountainous districts of Japan

Four aerial microalgae were isolated from the surface of rocks in mountainous districts of Japan and identified as Scenedesmus sp. KGU-Y002, Scenedesmus sp. KGU-D002, and Coelastrella sp. KGU-H001 of the class Chlorophyceae and Vischeria helvetica KGU-Y001 of the class Eustigmatophyceae based on 18S rDNA analysis. Algal carotenogenesis was enhanced by increasing the light intensity from 40 to 214μmol photonsm^-2s^-1, with more or less decrease in the total chlorophyll content. Culture of these microalgae under high-light conditions resulted in production of astaxanthin (free and esters), adonixanthin (free and esters), lutein, canthaxanthin, and β-carotene as the major carotenoids. Under high-light culture conditions, strains KGU-Y002, KGU-D002, KGU-H001, and KGU-Y001 accumulated 5.75, 10.45, 2.60, and 11.50mgg^-1 dry weight cells (dwc) of total carotenoids when the total chlorophyll contents were 3.51, 5.88, 2.91, and 7.17mgg^-1 dwc, respectively. The astaxanthin produced might primarily be synthesized from β-carotene via accumulation of zeaxanthin and adonixanthin in strains KGU-Y002, KGU-D002, and KGU-H001. Strain KGU-Y001 was found to accumulate astaxanthin and violaxanthin with large amounts of β-carotene. These results revealed that the biosynthesis pathways for astaxanthin in these isolates were significantly different from those of astaxanthin in green microalgae.