Production of high yields of docosahexaenoic acid byThraustochytrium roseum ATCC 28210

Thraustochytrids as a promising source of fatty acids, carotenoids, and sterols: bioactive compound biosynthesis, and modern biotechnology

Thraustochytrids are eukaryotes and obligate marine protists. They are increasingly considered to be a promising feed additive because of their superior and sustainable application in the production of health-benefiting bioactive compounds, such as fatty acids, carotenoids, and sterols. Moreover, the increasing demand makes it critical to rationally design the targeted products by engineering industrial strains. In this review, bioactive compounds accumulated in thraustochytrids were comprehensively evaluated according to their chemical structure, properties, and physiological function. Metabolic networks and biosynthetic pathways of fatty acids, carotenoids, and sterols were methodically summarized. Further, stress-based strategies used in thraustochytrids were reviewed to explore the potential methodologies for enhancing specific product yields. There are internal relationships between the biosynthesis of fatty acids, carotenoids, and sterols in thraustochytrids since they share some branches of the synthetic routes with some intermediate substrates in common. Although there are classic synthesis pathways presented in the previous research, the metabolic flow of how these compounds are being synthesized in thraustochytrids still remains uncovered. Further, combined with omics technologies to deeply understand the mechanism and effects of different stresses is necessary, which could provide guidance for genetic engineering. While gene-editing technology has allowed targeted gene knock-in and knock-outs in thraustochytrids, efficient gene editing is still required. This critical review will provide comprehensive information to benefit boosting the commercial productivity of specific bioactive substances by thraustochytrids.

Efficient co-production of EPA and DHA by Schizochytrium sp. via regulation of the polyketide synthase pathway

Presently, the supply of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) traditionally produced by marine fisheries will be insufficient to meet their market demand in food industry. Thus a sustainable alternative source is urgently required. Schizochytrium sp. is an ideal producer of DHA; however, its ability to co-produce DHA and EPA has not yet been proved. Herein, we first described a cobalamin-independent methionine synthase-like (MetE-like) complex, which contains independent acyltransferase and 3-ketoacyl synthase domains, independent of the traditional polyketide synthase (PKS) system. When the MetE-like complex was activated, the EPA content was increased from 1.26% to 7.63%, which is 6.06-folds higher than that in the inactivated condition. Through lipidomics, we find that EPA is more inclined to be stored as triglyceride. Finally, the EPA production was enhanced from 4.19 to 29.83 (mg/g cell dry weight) using mixed carbon sources, and the final yield reached 2.25 g/L EPA and 9.59 g/L DHA, which means that Schizochytrium sp. has great market potential for co-production of EPA and DHA.

Improved production of docosahexaenoic acid in batch fermentation by newly-isolated strains of Schizochytrium sp. and Thraustochytriidae sp. through bioprocess optimization

Thraustochytrids, rich in docosahexaenoic acid (DHA, C22:6ω3), represent a potential source of dietary fatty acids. Yet, the effect of culture conditions on growth and fatty acid composition vary widely among different thraustochytrid strains. Two different thraustochytrid strains, Schizochytrium sp. PKU#Mn4 and Thraustochytriidae sp. PKU#Mn16 were studied for their growth and DHA production characteristics under various culture conditions. Although they exhibited similar fatty acid profiles, PKU#Mn4 seemed a good candidate for industrial DHA fermentation while PKU#Mn16 displayed growth tolerance to a wide range of process conditions. Relative DHA content of 48.5% and 49.2% (relative to total fatty acids), respectively, were achieved on glycerol under their optimal flask culture conditions. Maximum DHA yield (Yp/x) of 21.0% and 18.9% and productivity of 27.6 mg/L-h and 31.9 mg/L-h were obtained, respectively, in 5-L bioreactor fermentation operated with optimal conditions and dual oxygen control strategy. A 3.4- and 2.8-fold improvement of DHA production (g/L), respectively, was achieved in this study. Overall, our study provides the potential of two thraustochytrid strains and their culture conditions for efficient production of DHA-rich oil.

Comparison of Thraustochytrids Aurantiochytrium sp., Schizochytrium sp., Thraustochytrium sp., and Ulkenia sp. for production of biodiesel, long-chain omega-3 oils, and exopolysaccharide

Heterotrophic growth of thraustochytrids has potential in coproducing biodiesel for transportation, as well as producing a feedstock for omega-3 long-chain (≥C20) polyunsaturated fatty acids (LC-PUFA), especially docosahexaenoic acid (DHA) for use in nutraceuticals. In this study, we compared eight new endemic Australian thraustochytrid strains from the genera Aurantiochytrium, Schizochytrium, Thraustochytrium, and Ulkenia for the synthesis of exopolysaccharide (EPS), in addition to biodiesel and LC-PUFA. Aurantiochytrium sp. strains readily utilized glucose for biomass production, and increasing glucose from 2 to 4 % w/v of the culture medium resulted in increased biomass yield by an average factor of 1.7. Ulkenia sp. strain TC 010 and Thraustochytrium sp. strain TC 033 did not utilize glucose, while Schizochytrium sp. strain TC 002 utilized less than half the glucose available by day 14, and Thraustochytrium sp. strain TC 004 utilized glucose at 4 % w/v but not 2 % w/v of the culture suggesting a threshold requirement between these values. Across all strains, increasing glucose from 2 to 4 % w/v of the culture medium resulted in increased total fatty acid methyl ester content by an average factor of 1.9. Despite an increasing literature demonstrating the capacity of thraustochytrids for DHA synthesis, the production of EPS from these organisms is not well documented. A broad range of EPS yields was observed. The maximum yield of EPS was observed for Schizochytrium sp. strain TC 002 (299 mg/L). High biomass-producing strains that also have high lipid and high EPS yield may be better candidates for commercial production of biofuels and other coproducts.

Thraustochytrids can be grown in low-salt media without affecting PUFA production

Marine microheterotrophs thraustochytrids are emerging as a potential source for commercial production of polyunsaturated fatty acids (PUFA) that have nutritional and pharmacological values. With prospective demand for PUFAs increasing, biotechnological companies are looking for potential increases in those valuable products. However, high levels of NaCl in the culture media required for optimal thraustochytrid growth and PUFA production poses a significant problem to the biotechnological industry due to corrosion of fermenters calling for a need to reduce the amount of NaCl in the culture media, without imposing penalties on growth and yield of cultured organisms. Earlier, as reported by Shabala et al. (Environ Microbiol 11:1835-1843, 2009), we have shown that thraustochytrids use sodium predominantly for osmotic adjustment purposes and, as such, can be grown in low-salt environment without growth penalties, providing the media osmolality is adjusted. In this study, we verify if that conclusion, made for one specific strain and osmolyte only, is applicable to the larger number of strains and organic osmotica, as well as address the issue of yield quality (e.g., PUFA production in low-saline media). Using mannitol and sucrose for osmotic adjustment of the growth media enabled us to reduce NaCl concentration down to 1 mM; this is 15-100-fold lower than any method proposed so far. At the same time, the yield of essential PUFAs was increased by 15 to 20 %. Taken together, these results suggest that the proposed method can be used in industrial fermenters for commercial PUFA production.

LC-PUFA from photosynthetic microalgae: occurrence, biosynthesis, and prospects in biotechnology

Microalgae offer potential for numerous commercial applications, among them the production of long-chain polyunsaturated fatty acids (LC-PUFAs). These valuable fatty acids are important for a variety of nutraceutical and pharmaceutical purposes, and the market for these products is continually growing. An appropriate ratio of LC-PUFA of the ω-3 and ω-6 groups is vital for "healthy" nutrition, and adequate dietary intake has strong health benefits in humans. Microalgae of diverse classes are primary natural producers of LC-PUFA. This mini-review presents an introductory overview of LC-PUFA-related health benefits in humans, describes LC-PUFA occurrence in diverse microalgal classes, depicts the major pathways of their biosynthesis in microalgae, and discusses the prospects for microalgal LC-PUFA production.

Widespread occurrence of secondary lipid biosynthesis potential in microbial lineages

Bacterial production of long-chain omega-3 polyunsaturated fatty acids (PUFAs), such as eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3), is constrained to a narrow subset of marine γ-proteobacteria. The genes responsible for de novo bacterial PUFA biosynthesis, designated pfaEABCD, encode large, multi-domain protein complexes akin to type I iterative fatty acid and polyketide synthases, herein referred to as "Pfa synthases". In addition to the archetypal Pfa synthase gene products from marine bacteria, we have identified homologous type I FAS/PKS gene clusters in diverse microbial lineages spanning 45 genera representing 10 phyla, presumed to be involved in long-chain fatty acid biosynthesis. In total, 20 distinct types of gene clusters were identified. Collectively, we propose the designation of "secondary lipids" to describe these biosynthetic pathways and products, a proposition consistent with the "secondary metabolite" vernacular. Phylogenomic analysis reveals a high degree of functional conservation within distinct biosynthetic pathways. Incongruence between secondary lipid synthase functional clades and taxonomic group membership combined with the lack of orthologous gene clusters in closely related strains suggests horizontal gene transfer has contributed to the dissemination of specialized lipid biosynthetic activities across disparate microbial lineages.

Microbial production of docosahexaenoic acid by a low temperature-adaptive strain Thraustochytriidae sp. Z105: screening and optimization

As an alternative source in addition to fish oil, microbial production of docosahexaenoic acid has been recieved more and more attentions owing to their culture advantage. A unicellular eukaryotic microbe with high DHA production and capable of low temperature-adaptive growth was isolated from seawater and identified as Thraustochytriidae sp. Z105. The siginificant effect of temperature on cell growth and DHA synthesis by the strain was revealed. It could grow and produce DHA even at 4 degrees C, but hardly grow above 35 degrees C. Low temperature (15-25 degrees C) was favorable for formation of biomass, lipids and DHA, but DHA synthesis was completely blocked above 30 degrees C. Conditions for high level DHA production by Thraustochytriidae sp. Z105 in flask culture were optimized as follows: medium containing glucose 80 g/l, yeast extract 5.0 g/l, K2HPO(4) . 3 H2O 1.0 g/l, MgSO4 . 7 H2O 0.5 g/l, seawater crystal 20 g/l, pH 6.0, liquid volume 30 ml/250 ml, temperature 20 degrees C, agitation speed of 200 r/min, and culture for 120 h. Under the optimal conditions, biomass of 16.72 g/l, total lipids of 5.35 g/l, DHA yield of 1.71 g/l (accounting for 32% of the total lipids) were achieved, respectively. In flask cluture level, the DHA productivity of Thraustochytriidae sp. Z105 was higher than most reported results, which suggested the wild type strain was a potential superior candidate for industrialization of DHA production. Moreover, the strain is an unique and valuable resource for investigation of the low temperature adaptive mechanism related to DHA synthesis.

Thraustochytrid Marine Protists: production of PUFAs and Other Emerging Technologies

Thraustochytrids, the heterotrophic, marine, straminipilan protists, are now established candidates for commercial production of the omega-3 polyunsaturated fatty acid (omega-3 PUFA), docosahexaenoic acid (DHA), that is important in human health and aquaculture. Extensive screening of cultures from a variety of habitats has yielded strains that produce at least 50% of their biomass as lipids, and DHA comprising at least 25% of the total fatty acids, with a yield of at least 5 g L(-1). Most of the lipids occur as triacylglycerols and a lesser amount as phospholipids. Numerous studies have been carried out on salinity, pH, temperature, and media optimization for DHA production. Commercial production is based on a fed batch method, using high C/N ratio that favors lipid accumulation. Schizochytrium DHA is now commercially available as nutritional supplements for adults and as feeds to enhance DHA levels in larvae of aquaculture animals. Thraustochytrids are emerging as a potential source of other PUFAs such as arachidonic acid and oils with a suite of PUFA profiles that can have specific uses. They are potential sources of asataxanthin and carotenoid pigments, as well as other lipids. Genes of the conventional fatty acid synthesis and the polyketide-like PUFA synthesis pathways of thraustochytrids are attracting attention for production of recombinant PUFA-containing plant oils. Future studies on the basic biology of these organisms, including biodiversity, environmental adaptations, and genome research are likely to point out directions for biotechnology explorations. Potential areas include enzymes, polysaccharides, and secondary metabolites.

The effect of dietary docosahexaenoic acid on the expression of lipogenic genes in broilers

The objectives of this work were to determine the effects of dietary fungal docosahexaenoic acid (DHA) on tissue DHA concentration and lipogenic gene expression in broilers. A fungal (SR-21) meal product containing 31.5% total fat and 32.7% DHA (% of total fatty acids) was fed to chicken broilers at 0, 1, or 3% for 3 weeks. A diet with 1% DHA oil (containing 40% DHA) was also fed to chicken broilers as a positive control. Dietary fungal meal supplementation (3%) improved daily weight gain, food intake, and feed conversion ratio. The fungal meal supplementation increased dietary DHA content and consequently increased the DHA content in plasma, breast muscle (Pectoralis major), and livers in the broilers. The plasma triacylglycerol concentration was decreased by the supplementation of dietary DHA. The data indicate that the dietary DHA treatment modified certain aspects of the lipid metabolism, especially pathways related to triacylglycerol synthesis. Indeed, both the 1% DHA oil and 3% fungal meal treatments decreased the hepatic lipogenic transcription factor sterol regulatory element binding protein 1 (SREBP1) mRNA relative abundance, suggesting that dietary DHA supplementation decreases SREBP1 gene functions. The relative mRNA abundance of the de novo fatty acid synthesis genes, fatty acid synthase and acetyl coenzyme A carboxylase, was reduced by 1% DHA oil and 3% fungal meal treatments, suggesting that dietary DHA supplementation decreases lipogenesis in the livers of the broilers. Taken together, the fungal meal is a suitable dietary supplement to increase tissue DHA content and reduce the expression of hepatic lipogenic genes in broilers.

Isolation and characterization of a novel thraustochytrid-like microorganism that efficiently produces docosahexaenoic acid

A thraustochytrid-like microorganism (strain 12B) was isolated from the mangrove area of Okinawa, Japan. On the basis of its ectoplasmic net structure and biflagellate zoospores we determined strain 12B to be a novel member of the phylum Labyrinthulomycota in the kingdom Protoctista. When grown on glucose/seawater at 28 degrees C, it had a lipid content of 58% with docosahexaenoic acid (DHA; 22:6 n-3) at 43% of the total fatty acids. It had a growth rate of 0.38 h(-1). The DHA production rate of 2.8 +/- 0.7 g l(-1) day(-1) is the highest value reported for any microorganism.

Schizochytrium limacinum SR-21 as a source of docosahexaenoic acid: optimal growth and use as a dietary supplement for laying hens

Culture conditions for the marine fungus Schizochytrium limacinum SR-21 (SR-21) to produce microbial docosahexaenoic acid (DHA) were evaluated, and the practicality of using this fungus product as a dietary supplement for laying Leghorn hens was investigated. The data showed that the cultured fungus produced high biomass and DHA. It generated 584 mg DHA/L of culture at the end of a 6-day culture. The fungus grew better at 25ºC than at 20ºC or 30ºC. With an increase in glucose concentration from 1% to 5% in the culture medium, biomass and DHA production were enhanced. A 6% glucose treatment reduced the biomass production compared with 5% glucose. A bioreactor was used to mass-produce SR-21. The biomass was increased from 1.12 g/L at Day 0 to 12 g/L at Day 4. We established optimal culture conditions of 5% glucose, 2% sea salt, and 1% yeast extract for SR-21. Three concentrations of dried fungal meal (0, 1, or 3% in the diet) were fed to birds over a 3-week period. There were no negative effects of 1 and 3% dietary SR-21 on egg production, egg weight, and egg yolk weight. The DHA content of yolk was increased by the dietary supplementation with the fungal meal both in the 1 and 3% treatments. Dietary fungal meal treatments increased the DHA concentrations of liver and plasma. However, dietary DHA enrichment had no effect on the expression of hepatic lipogenic genes in laying hens.

Fatty acids from lipids of marine organisms: molecular biodiversity, roles as biomarkers, biologically active compounds, and economical aspects

Because of their characteristic living environments, marine organisms produce a variety of lipids. Fatty acids constitute the essential part of triglycerides and wax esters, which are the major components of fats and oils. Nevertheless, phospholipids and glycolipids have considerable importance and will be taken into account, especially the latter compounds that excite increasing interest regarding their promising biological activities. Thus, in addition to the major polyunsaturated fatty acids (PUFA) such as eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids, a great number of various fatty acids occur in marine organisms, e.g. saturated, mono- and diunsaturated, branched, halogenated, hydroxylated, methoxylated, non-methylene-interrupted. Various unprecedented chemical structures of fatty acids, and lipid-containing fatty acids, have recently been discovered, especially from the most primitive animals such as sponges and gorgonians. This review of marine lipidology deals with recent advances in the field of fatty acids since the end of the 1990s. Different approaches will be followed, mainly developing biomarkers of trophic chains in marine ecosystems and of chemotaxonomic interest, reporting new structures, especially those with biological activities or biosynthetic interest. An important part of this review will be devoted to the major PUFA, their relevance to health and nutrition, their biosynthesis, their sources (usual and promising) and market.