Namibia Workshop Presentations

Presenter: Ami Ben Amotz

Glycerol

• Dunaliella adapts to high extracellular osmotic stress by synthesis of very high content of intracellular cytosolic glycerol, different than halobacteria which accumulate ions.
• Glycerol is produced either photosynthetically by carbon dioxide or by degradation of intracellular starch reserves.
• The induction of glycerol synthesis or reassimilation is triggered by cell volume changes.
• Activation of glycerol synthesis does not involve de novo protein biosynthesis. Glycerol phosphate dehydrogenase, dihydroxyacetone phosphate reductase and phosphofructokinase are probably the checkpoint enzymes which control glycerol synthesis.
• The molecular mechanism which triggers glycerol production in Dunaliella is not yet known. Changes in the plasma membrane, inorganic phosphate, and pH following osmotic shocks suggest that plasma membrane sensors as well as soluble metabolites are involved in the activation of glycerol synthesis.

Beta-Carotene

• Dunaliella adapts to high solar radiation by the accumulation of high content of chloroplastic peripheral extra-plastidic beta-carotene acting as light screen to prevent photooxidation.
• The beta-carotene of Dunaliella is composed of two stereoisomers, all-trans and 9-cis reaching a ratio of 1/1 under certain growth conditions.
• The beta-carotene of Dunaliella is stored within distinguished oil globules of special lipid profile.
• The content of beta-carotene and the isomeric ratio in the algal oily globules is manipulated and regulated by external environmental stimuli such as salt, light, nutrients and temperature.

Biotechnology
Currently Dunaliella is one of the very few microalgae that are commercially exploited. Although it is now cultivated intensively mainly for beta-carotene production, Dunaliella can grow autotrophically also extensively on carbon dioxide for the production of both glycerol and beta-carotene. The ability to use natural resources of sea and salt water, arid land, flue gas and solar radiation on wide global distribution makes this halo tolerant alga most attractive for open cultivation and commercialization for bioenergy and natural products.