Metabolic fingerprinting of Dunaliella salina cultured under sulfur deprivation conditions

Dunaliella salina is the major commercial source of natural beta-carotene. Limitation of key macronutrients, such as sulfur, in the late stages of D. salina cultivation is one of the main inducers of mass accumulation of beta-carotene. In this study the nutritional changes and metabolic responses of D. salina to sulfur deprivation were investigated by gas chromatography-mass spectrometry. A total of 82 significantly influenced metabolites were identified in cells cultured in either sulfur-deprived or sulfur-replete media, including 19 amino acids, 19 sugars, 26 organic acids, 12 alcohols, 5 amines, and phosphate. The metabolites were categorized into three groups by hierarchical clustering based on their change trends. Partial least squares and principal component analyses showed that a large number of metabolic pathways of D. salina cells cultured under sulfur deprivation conditions changed significantly. Twenty-one metabolites were identified as biomarkers that can be used to distinguish the cells cultivated under sulfur-replete and sulfur-depleted conditions. There was a decrease of total free fatty acid contents, accompanied by increased content of saturated and decreased content of unsaturated fatty acids. The increases of most amino acids, sugars, and 2-ketoglutaric acid, together with the decrease of total fatty acids, indicate that carbon units from protein metabolism were mainly diverted into starch biosynthesis, together with the products of photosynthesis. This study contributes to the elucidation of the metabolic mechanisms triggered in D. salina upon sulfur deprivation, offering insights into nutrition optimization for the cultivation of D. salina, with the aim of increasing the production of natural carotenoids.