Massive accumulation of beta-carotene green alga Dunaliella salina induced by variation of nitrate and salinity
1999
Haouazine, Y. | Riyahi, J. | Mouradi, A. (Universite Ibn Tofail, Kenitra (Morocco). Lab. de biochimie et de biotechnologies marines) | Rmiki, N. | Givernaud, T. | Lemoine, Y.
Dunaliella salina Teodoresco, a beta-carotene-accumulating halotolerant green alga, was isolated from commercial salt fields (Societe sherifienne des sels, Larache, Morocco) and analyzed for the effects of various growth conditions on its pigment content and on the stereoisomeric composition of beta-carotene by HPLC. Cultures were grown under differents nutrients concentrations (NaNO3, NaCl), under a continuous photon flux density 40 micromol photon per square m per s at 32øC with aeration. Total carotenoid content was measured during the exponential growth phase. Nitrate concentrations upper than 1.5 mM gave cultures with the highest growth rate and the lowest total carotenoid content. Below 1.5 mM nitrate, culture exibited the lowest growth rate and accumulated the highest total carotenoid content. Salinity is a factor limiting growth in Dunaliella salina. An increase of salinity resulted a decreased growth rate and an increase of total carotenoids. This increase in total carotenoids results from an increase in the proportion of beta-carotene and alpha-carotene. In Dunaliella salina, inhibiting growth by various stress conditions (nutrient deficiency or high salt concentration) caused an increase in the amount of beta-carotene per cell. As a result, the beta-carotene-to-chlorophyll ratio increased and the alga changed its visual appearance from green to yellowish. Analysis of the pigments by HPLC showed that the beta-carotene was composed by two major isomers: all-trans beta-carotene and 9-cis beta-carotene.
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