Carotenoids and metabolism of the green microalga Chlorococcum sp. 8367RE under stress conditions

Abstract

Green microalgae are one of the natural resources for productions of various and beneficial bioactive compounds, such as UV-screening compounds and carotenoids. This study focuses on the changes of carotenoids and metabolisms in the green microalga Chlorococcum sp. 8367RE under stress conditions. The results showed that stresses by salt, light, drought, and nitrogen starvation affected on alterations of morphological characteristics. Interestingly, size of cells culturing under salt stresses dramatically increased. It should be noted that KCl stress caused the enlargement of cell sizes approximately 5 folds. Carotenoids were identified and quantified by using ultra-high performance liquid chromatography (UHPLC) and mass spectrometry. Three kinds of carotenoids namely violaxanthin, antheraxanthin and lutein were found in algal extracts culturing under control condition. Among these carotenoids, lutein was detected as the highest content 2.24 μg/mg DW. Upon KCl stress, two types of carotenoids; astaxanthin and canthaxanthin, were additionally identified. It is noteworthy that this stress condition, lutein content was very similar level as control while astaxanthin was accumulated 0.12 μg/mg DW. For nitrogen starvation, total carotenoids were decreased. Furthermore, fatty acids, proteins, amino acids, and carbohydrates were analyzed. KCl stress and nitrogen starvation led to the increment of fatty acids contents approximately 2 times (12.79 ± 0.03% DW) and 4 times (28.07 ± 0.79% DW), respectively. Oleic acid was found to be the predominant fatty acid. This study indicates that salt stress resulted in the remarkable alteration of cells morphology and the enhancement of valuable secondary carotenoids and omega-9 fatty acid accumulation. These would be advantageous in health and nutraceutical industries.