Carotenogenesis and carotenoid esterification in biofilms of the microalga Coelastrella rubescens KGU-Y002 in the aerial phase

Abstract

Water supply, light intensity, and the light spectrum are important parameters that affect the growth of microalgae, but their influence on cultivation of carotenoid-rich microalgae in aerial conditions has not been thoroughly studied. In this work, the effects of water supply, light intensity, and the applied light spectrum on aerial-phase biofilms of the aerial microalga Coelastrella rubescens KGU-Y002 were investigated. First, the appropriate supply of water was investigated. In the presence of sufficient water, the microalga (1 g dry cell weight) consumed approximately 50 g of water in 7 days of culture. It was necessary to supply 8.8 mL g−1 d−1 of water to the biofilm to maintain biological activity. In aerial conditions, the microalga was able to fix carbon dioxide for biosynthesis of carotenoids and fatty acids. Next, the effect of light intensity was examined. The total and ester-type carotenoid contents were highest on illumination at 100 μmol photons m−2 s−1; after 7 days, they were 2.4- and 2.1-times those at the start of culture, respectively. The effect of light wavelength from light emitting diodes (LEDs) on carotenoid accumulation and esterification in the microalga was investigated. When the biofilm was irradiated using red LEDs, the contents of total carotenoids and carotenoid esters were increased approximately three and nine times, respectively, after 7 days compared with those at the start of the culture. Because fatty acids were synthesized, ester-type carotenoids were efficiently synthesized. Blue light promoted cell division and increased the total fatty acid content but decreased the total carotenoid content compared with red or green light. For carotenoid production from the microalga C. rubescens in aerial phase conditions, the cells under blue light can be proliferated, and then switched to red-light illumination to promote carotenoid biosynthesis.