Thraustochytrids as production organisms for docosahexaenoic acid (DHA), squalene, and carotenoids

Abstract

Thraustochytrids have been applied for industrial production of the omega-3 fatty acid docosahexaenoic (DHA) since the 1990s. During more than 20 years of research on this group of marine, heterotrophic microorganisms, considerable increases in DHA productivities have been obtained by process and medium optimization. Strains of thraustochytrids also produce high levels of squalene and carotenoids, two other commercially interesting compounds with a rapidly growing market potential, but where yet few studies on process optimization have been reported. Thraustochytrids use two pathways for fatty acid synthesis. The saturated fatty acids are produced by the standard fatty acid synthesis, while DHA is synthesized by a polyketide synthase. However, fundamental knowledge about the relationship between the two pathways is still lacking. In the present review, we extract main findings from the high number of reports on process optimization for DHA production and interpret these in the light of the current knowledge of DHA synthesis in thraustochytrids and lipid accumulation in oleaginous microorganisms in general. We also summarize published reports on squalene and carotenoid production and review the current status on strain improvement, which has been hampered by the yet very few published genome sequences and the lack of tools for gene transfer to the organisms. As more sequences now are becoming available, targets for strain improvement can be identified and open for a system-level metabolic engineering for improved productivities.

Comparative Transcriptomic Analysis Uncovers Genes Responsible for the DHA Enhancement in the Mutant Aurantiochytrium sp.

“…Approximately 200,000 tons of fish oils are used in products for the human markets. Meanwhile, the production of microbial n-3-rich oils constituted only 5000 tons in 2011, with marine protist Thraustochytrids and the heterotrophic microalgae Chrypthecodinium cohnii as production organisms [34]. Although industrial DHA production has been accomplished, certain approaches have been applied to enhance the synthesis of DHA via intrinsic [61,62] or extrinsic parameters [63].…”

“…[33]. Recent research has indicated that DHA is synthesized by two distinct pathways in Thraustochytrids: The polyketide synthase (PKS) pathway and the fatty acid synthase (FAS) pathway [34]. Fatty acids are synthesized through the PKS pathway via highly repetitive cycles of four reactions, including condensation by ketoacyl synthase (KS), ketoreduction (KR), dehydration, and enoyl reduction (ER) [35].…”

Marine Microbial-Derived Molecules and Their Potential Use in Cosmeceutical and Cosmetic Products

“…Besides photosynthetic organisms, heterotrophic bacteria and marine fungi (especially pigmented yeasts), thraustochytrids (generally defined as fungi-like protists) are also a relevant source of carotenoids [28,29,30,33]. However, these microorganisms have not been examined as extensively as the photosynthetic organisms (i.e., algae) for the production of carotenoids [106].…”

“…and Aurantiochytrium sp. KH105 synthesize different carotenoids including β-carotene, astaxanthin, zeaxanthin, cantaxanthin, phoenicoxanthin and echinenone [33]. Engineering approaches have allowed the increase in production of carotenoids (even nine-fold increased astaxanthin content production) such as in Aurantiochytrium sp.…”

“…In particular, there is evidence that species belonging to Schizochytrium , Aurantiochytrium and Ulkenia isolated from several marine ecosystems, including sandy beaches and mangrove forests, are the major producers of DHA [52]. DHA-rich oils from thraustochytrids are currently on the market particularly for applications in nutraceuticals and aquaculture [33]. However, they also have a great potential for cosmetic and cosmeceutical applications.…”