Metabolic responses and β-carotene production by the unicellular green alga Dunaliella salina exposed to leaf extracts

ABSTRACT

The present work investigated the effects of aqueous extracts of eucalyptus ( Eucalyptus globulus) and elderberry ( Sambucus ebulus) leaves on β-carotene productivity in Dunaliella salina, a green microalga. Leaf extracts from eucalyptus have greater amounts of phenolics and flavonoids, as well as greater ferric reducing antioxidant potential than elderberry. The extracts of both species greatly inhibited growth of algal suspensions. However, chlorophyll and β-carotene concentration increased in cells treated with leaf extracts, and the highest values were detected in 1 % eucalyptus and 2 % elderberry extracts. Fresh weight, total sugar, and protein content significantly increased following exposure of cells to different doses of leaf extracts. However, in doses containing more than 2 % eucalyptus, the upward trend for total sugar and protein ceased and remained statistically unchanged. These results suggest that metabolic modifications enable D. salina cells to tolerate the stress induced by the leaf extracts through allocating carbon flux to the synthesis of osmolytes and putative antioxidant molecules (e.g. sugars and β-carotene). Therefore, the use of leaf extracts holds potential to be a promising and effective way to improve D. salina cultivation for β-carotene production and other biotechnological and industrial applications.

Keywords
β-carotene; Dunaliella salina; eucalyptus; elderberry; leaf extracts; metabolites; stress