Carotenoid production and change of photosynthetic functions in Scenedesmus sp exposed to nitrogen limitation and acetate treatment

Under stress conditions, some microalgae up-regulate certain biosynthetic pathways, leading to the accumulation of specific compounds. For example, changing nutrient composition can induce stress in algae's physiological activities, which may trigger an intense increase in carotenoid production. In this study, the change of photosynthetic functions and carotenoid production in the green microalga Scenedesmus sp. was investigated when algal cultures were exposed to conditions including limited nitrogen content with the addition of sodium acetate. Microalgal cultures were treated for 18 days under higher irradiance conditions. We observed a decrease of chlorophyll content induced concomitantly with a decline of photosystem II and I photochemistry. At the same time, an important increase in carotenoid content was detected. By using high-performance liquid chromatographic analysis, we found that the secondary carotenoids astaxanthin and canthaxanthin were accumulated compared to controls. During the process of carotenoid accumulation, chlorophyll degradation was found in addition to a strong decrease in photosynthetic electron transport. Such changes may be associated with the structural reorganization of the photosynthetic apparatus and can be a useful indicator of secondary carotenoid accumulation in algal cultures.