Antarctic Thraustochytrids as Sources of Carotenoids and High-Value Fatty Acids

Abstract

Eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and carotenoids are needed as human dietary supplements and are essential components in commercial feeds for the production of aquacultured seafood. Microorganisms such as thraustochytrids are potential natural sources of these compounds. This research reports on the lipid and carotenoid production capacity of thraustochytrids that were isolated from coastal waters of Antarctica. Of the 22 isolates, 21 produced lipids containing EPA+DHA, and the amount of these fatty acids exceeded 20% of the total fatty acids in 12 isolates. Ten isolates were shown to produce carotenoids (27.4–63.9 μg/g dry biomass). The isolate RT2316-16, identified as Thraustochytrium sp., was the best producer of biomass (7.2 g/L in five days) rich in carotenoids (63.9 μg/g) and, therefore, became the focus of this investigation. The main carotenoids in RT2316-16 were β-carotene and canthaxanthin. The content of EPA+DHA in the total lipids (34 ± 3% w/w in dry biomass) depended on the stage of growth of RT2316-16. Lipid and carotenoid content of the biomass and its concentration could be enhanced by modifying the composition of the culture medium. The estimated genome size of RT2316-16 was 44 Mb. Of the 5656 genes predicted from the genome, 4559 were annotated. These included genes of most of the enzymes in the elongation and desaturation pathway of synthesis of ω-3 polyunsaturated fatty acids. Carotenoid precursors in RT2316-16 were synthesized through the mevalonate pathway. A β-carotene synthase gene, with a different domain organization compared to the gene in other thraustochytrids, explained the carotenoid profile of RT2316-16.

Production of Carotenoids and Phospholipids by Thraustochytrium sp. in Batch and Repeated-Batch Culture

“…Biotin and ascorbic acid were found to have little or no effect on biomass growth and lipid synthesis. A lack of a biotin effect was possibly due to its endogenous synthesis: a search of the genome data of RT2316-16 [ 15 ] revealed the presence of most genes for the enzymes of the biotin biosynthesis pathway. The relatively minor effects of ascorbic acid on the growth of lipid-free biomass and total carotenoids in the biomass depended on the carbon source.…”

“…Therefore, an enhanced activity of mGPDH in cells grown on glycerol does explain their elevated total carotenoids level compared to cells grown on glucose ( Figure 1 a). In the genome of RT2316-16, gene sequences for a glycerol-3-phosphate dehydrogenase (Thraus_T878) and two mGPDH (Thraus_T1613 and T1688) have been annotated [ 15 ], suggesting that glycerophosphate shuttle may indeed be active in this microorganism.…”

“…The present work focused on establishing the effects of culture conditions (nutrients in the culture medium, temperature and illumination) on the production of lipids (total lipids and phospholipid) and total carotenoids by Thraustochytrium sp. RT2316-16, an Antarctic thraustochytrid capable of producing β-carotene and canthaxanthin [ 15 ]. The microorganism was grown in batch and repeated-batch cultures.…”

Chemical and Physical Culture Conditions Significantly Influence the Cell Mass and Docosahexaenoic Acid Content of Aurantiochytrium limacinum Strain PKU#SW8

“…Although a large number of thraustochytrids, isolated from a range of marine habitats, have been reported recently [4][5][6][7][8], the culture conditions of only some of these isolates have been optimized so far for their biotechnological potential. Indeed, to improve the cell mass and DHA content, the optimization of culture conditions is imperative.…”

Exogenous Antioxidants Improve the Accumulation of Saturated and Polyunsaturated Fatty Acids in Schizochytrium sp. PKU#Mn4

“…Thraustochytrids are marine unicellular heterotrophic protists that can naturally accumulate lipids up to 55% of their dry biomass [1] and are promising cell factories for highvalue polyunsaturated fatty acids (PUFA), saturated fatty acids (SFA), and terpenoids [2]. The thraustochytrid strains belonging to genera Aurantiochytrium, Schizochytrium, and Thraustochytrium are particularly known for their extraordinary ability to produce lipids during glucose or glycerol fermentation [3][4][5][6]. Over the past two decades, several strategies towards enhancing the production of high-value fatty acids in oleaginous thraustochytrids were reported [7][8][9][10][11][12].…”