Accumulation of -carotene in halotolerant algae purification and characterization of -carotene-rich globules from Dunaliella bardawil

Ben-Amotz, A.; Katz, A.; Avron, M.

Journal of Phycology 184: 529-537


ISSN/ISBN: 0022-3646
Accession: 037747212

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D. bardawil Ben-Amotz et Avron, but not most other Dunaliella species, has a unique property of being able to accumulate, in addition to glycerol, large amounts of .beta.-carotene when cultivated under appropriate conditions. These include high light intensity, a high NaCl concentration, nitrate deficiency and extreme temperatures. Under conditions of maximal carotene accumulation D. bardawil contains at least 8% of its dry wt as .beta.-carotene while D. salina grown under similar conditions contains only .apprx. 0.3%. Electron micrographs of D. bardawil grown under conditions of high .beta.-carotene accumulation show many .beta.-carotene containing globules located in the interthylakoid spaces of the chloroplast. The same algae grown under conditions where .beta.-carotene does not accumulate contain few to no .beta.-carotene globules. The .beta.-carotene-rich globules were released from the algae into an aqueous medium by a 2-stage osmotic shock technique and further purified by centrifugation on 10% sucrose. The isolated purified globules were shown by EM to be free of significant contamination and composed of membrane-free osmiophilic droplets with an average diameter of 150 nm. Reversed phase high performance liquid chromatography HPLC of a total pigment extract of the cells revealed the presence of .beta.-carotene as the major pigment, together with chlorophylls a and b, .alpha.-carotene and the xanthophylls lutein, neoxanthin and zeaxanthin. .beta.-Carotene accounted for essentially all the pigment in the purified globules. Analysis of the algal and globule .beta.-carotene fractions by HPLC showed that the .beta.-carotene was composed of appr. equal amounts of all-trans .beta.-carotene and of its 9-cis isomer. Intact D. bardawill cells contained on a dry wt basis .apprx. 30% glycerol, 30% protein, 18/% lipid, 11% carbohydrate, 9% .beta.-carotene and 1% chlorophyll.