isolated from Yap Islands

The Nitrogen Content in the Fruiting Body and Mycelium of Pleurotus Ostreatus and Its Utilization as a Medium Component in Thraustochytrid Fermentation

Following the idea of a circular bioeconomy, the use of side streams as substitutes for cultivation media (components) in bioprocesses would mean an enormous economic and ecological advantage. Costly compounds in conventional media for the production of the triterpene squalene in thraustochytrids are the main carbon source and complex nitrogen sources. Among other side streams examined, extracts from the spent mycelium of the basidiomycete Pleurotus ostreatus were best-suited to acting as alternative nitrogen sources in cultivation media for thraustochytrids. The total nitrogen (3.76 ± 0.01 and 4.24 ± 0.04%, respectively) and protein (16.47 ± 0.06 and 18.57 ± 0.18%, respectively) contents of the fruiting body and mycelium were determined. The fungal cells were hydrolyzed and extracted to generate accessible nitrogen sources. Under preferred conditions, the extracts from the fruiting body and mycelium contained 73.63 ± 1.19 and 89.93 ± 7.54 mM of free amino groups, respectively. Cultivations of Schizochytrium sp. S31 on a medium using a mycelium extract as a complex nitrogen source showed decelerated growth but a similar squalene yield (123.79 ± 14.11 mg/L after 216 h) compared to a conventional medium (111.29 ± 19.96 mg/L, although improvable by additional complex nitrogen source).

Evaluation of Growth Performance and Environmental Impact of Hermetia illucens Larvae Reared on Coffee Silverskins Enriched with Schizochytrium limacinum or Isochrysis galbana Microalgae

Hermetia illucens is a promising insect due to its ability to convert low-value substrates as food chain by-products into highly nutritious feed. Its feeding and nutrition are important issues. The aim of this work was to investigate the effect of different substrates consisting of coffee silverskin, a by-product of the roasting process, enriched with different inclusions of microalgae (5%, 10%, 20%, and 25%), Schizochytrium limacinum, and Isochrysis galbana, combined with the assessment of environmental sustainability by LCA. In general, the addition of microalgae led to an increase in larval growth performance due to the higher content of protein and lipids, although S. limacinum showed the best results with respect to larvae fed with coffee silverskin enriched with I. galbana. A higher prepupal weight was observed in larvae fed with 10%, 20%, and 25% S. limacinum; shorter development times in larvae fed with 25% of both S. limacinum and I. galbana; and a higher growth rate in larvae fed with 25% S. limacinum. The 10% S. limacinum inclusion was only slightly different from the higher inclusions. Furthermore, 10% of S. limacinum achieved the best waste reduction index. The greater the inclusion of microalgae, the greater the environmental impact of larval production. Therefore, the addition of 10% S. limacinum appears to be the best compromise for larval rearing, especially considering that a higher inclusion of microalgae did not yield additional benefits in terms of the nutritional value of H. illucens prepupae.

Enhancing the accumulation of lipid and docosahexaenoic acid in Schizochytrium sp. by co-overexpression of phosphopantetheinyl transferase and ω-3 fatty acid desaturase

Docosahexaenoic acid (DHA) as one of ω-3 polyunsaturated fatty acids (PUFAs), plays a key role in brain development, and is widely used in food additives and the pharmaceutical industry. Schizochytrium sp. is often considered as a satisfactory strain for DHA industrialization. The aim of this study was to assess the feasibility of phosphopantetheinyl transferase (PPTase) and ω-3 fatty acid desaturase (FAD) for regulating DHA content in Schizochytrium sp. PPTase is essential to activate the polyketide-like synthase (PKS) pathway, which can transfer apo-acyl-carrier protein (apo-ACP) into holo-ACP, and plays a key role in DHA synthesis. Moreover, DHA and docosapentaenoic acid (DPA) are synthesized by the PKS pathway simultaneously, so high DPA synthesis limits the increase of DHA content. In addition, the detailed mechanisms of PKS pathway have not been fully elucidated, so it is difficult to improve DHA content by modifying PKS. However, ω-3 FAD can convert DPA into DHA, and it is the most direct and effective way to increase DHA content and reduce DPA content. Based on this, PPTase was overexpressed to enhance the synthesis of DHA by the PKS pathway, overexpressed ω-3 FAD to convert the co-product of the PKS pathway into DHA, and co-overexpressed PPTase and ω-3 FAD. With these strategies, compared with wild type, the final lipid, and DHA titer were 92.5 and 51.5 g L-1 , which increased by 46.4% and 78.1%, respectively. This study established an efficient DHA production strain, and provided some feasible strategies for industrial DHA production in Schizochytrium sp.

Production of docosahexaenoic acid from spruce sugars using Aurantiochytrium limacinum

In this study lignocellulosic sugars from Norway spruce were used for production of docosahexaenoic acid (DHA) by the marine thraustochytrid Aurantiochytrium limacinum SR21. Enzymatically prepared spruce hydrolysate was combined with a complex nitrogen source and different amounts of salts. Shake flask batch cultivations revealed that addition of extra salts was not needed for optimal growth. Upscaling to fed-batch bioreactors yielded up to 55 g/L cell dry mass and a total fatty acid content of 44% (w/w) out of which 1/3 was DHA. Fourier transform infrared spectroscopy was successfully applied as a rapid method for monitoring lipid accumulation in A. limacinum SR21. Thus, this proof-of-principle study clearly demonstrates that crude spruce hydrolysates can be directly used as a novel and sustainable resource for production of DHA.

Protist–Lactic Acid Bacteria Co-Culture as a Strategy to Bioaccumulate Polyunsaturated Fatty Acids in the Protist Aurantiochytrium sp. T66

Thraustochytrids are aquatic unicellular protists organisms that represent an important reservoir of a wide range of bioactive compounds, such as essential polyunsaturated fatty acids (PUFAs) such as arachidonic acid (ARA), docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), which are involved in the regulation of the immune system. In this study, we explore the use of co-cultures of Aurantiochytrium sp. and bacteria as a biotechnological tool capable of stimulating PUFA bioaccumulation. In particular, the co-culture of lactic acid bacteria and the protist Aurantiochytrium sp. T66 induce PUFA bioaccumulation, and the lipid profile was evaluated in cultures at different inoculation times, with two different strains of lactic acid bacteria capable of producing the tryptophan dependent auxins, and one strain of Azospirillum sp., as a reference for auxin production. Our results showed that the Lentilactobacillus kefiri K6.10 strain inoculated at 72 h gives the best PUFA content (30.89 mg g−1 biomass) measured at 144 h of culture, three times higher than the control (8.87 mg g−1 biomass). Co-culture can lead to the generation of complex biomasses with higher added value for developing aquafeed supplements.

Microbes: A Hidden Treasure of Polyunsaturated Fatty Acids

Microbes have gained a lot of attention for their potential in producing polyunsaturated fatty acids (PUFAs). PUFAs are gaining scientific interest due to their important health-promoting effects on higher organisms including humans. The current sources of PUFAs (animal and plant) have associated limitations that have led to increased interest in microbial PUFAs as most reliable alternative source. The focus is on increasing the product value of existing oleaginous microbes or discovering new microbes by implementing new biotechnological strategies in order to compete with other sources. The multidisciplinary approaches, including metabolic engineering, high-throughput screening, tapping new microbial sources, genome-mining as well as co-culturing and elicitation for the production of PUFAs, have been considered and discussed in this review. The usage of agro-industrial wastes as alternative low-cost substrates in fermentation for high-value single-cell oil production has also been discussed. Multidisciplinary approaches combined with new technologies may help to uncover new microbial PUFA sources that may have nutraceutical and biotechnological importance.

Isolation and characterization of the ω3-docosapentaenoic acid-producing microorganism Aurantiochytrium sp. T7

ω3-Docosapentaenoic acid (ω3-DPA), an ω3-polyunsaturated fatty acid (ω3-PUFA), is expected to have beneficial physiological functions to humans; however, because of its rarity in nature, it has not been fully analyzed. We isolated an ω3-DPA producing microorganism strain T7 from brackish areas in Japan. Although most oleaginous microorganisms rarely accumulate ω3-DPA (<5% of total lipid), strain T7 accumulated ω3-DPA with more than 20% of total fatty acids. The strain T7 was identified as a related species of Aurantiochytrium. In Aurantiochytrium sp. T7, ω3-DPA production reached 164 mg/L culture broth, and the ω3-DPA content reached 23.5% of the total fatty acids when cultivated in a medium containing 2% glucose as the carbon source and 1% yeast extract as the nitrogen source, with a salinity equivalent to 50% of that of seawater and a pH in the acidic range (pH < 5.5). Aurantiochytrium sp. T7 is a promising producer of high-purity ω3-DPA containing-lipid for the functional analysis of ω3-DPA whose physiological function has hardly been elucidated, and a useful strain for investigating the novel metabolic pathway of fatty acids.

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

Thraustochytrids are well-known unicellular heterotrophic marine protists because of their promising ability to accumulate docosahexaenoic acid (DHA). However, the implications of their unique genomic and metabolic features on DHA production remain poorly understood. Here, the effects of chemical and physical culture conditions on the cell mass and DHA production were investigated for a unique thraustochytrid strain, PKU#SW8, isolated from the seawater of Pearl River Estuary. All the tested fermentation parameters showed a significant influence on the cell mass and concentration and yield of DHA. The addition of monosaccharides (fructose, mannose, glucose, or galactose) or glycerol to the culture medium yielded much higher cell mass and DHA concentrations than that of disaccharides and starch. Similarly, organic nitrogen sources (peptone, yeast extract, tryptone, and sodium glutamate) proved to be beneficial in achieving a higher cell mass and DHA concentration. PKU#SW8 was found to grow and accumulate a considerable amount of DHA over wide ranges of KH2PO4 (0.125-1.0 g/L), salinity (0-140% seawater), pH (3-9), temperature (16-36 °C), and agitation (140-230 rpm). With the optimal culture conditions (glycerol, 20 g/L; peptone, 2.5 g/L; 80% seawater; pH 4.0; 28 °C; and 200 rpm) determined based on the shake-flask experiments, the cell mass and concentration and yield of DHA were improved up to 7.5 ± 0.05 g/L, 2.14 ± 0.03 g/L, and 282.9 ± 3.0 mg/g, respectively, on a 5-L scale fermentation. This study provides valuable information about the fermentation conditions of the PKU#SW8 strain and its unique physiological features, which could be beneficial for strain development and large-scale DHA production.

Production of Omega-3 Oil by Aurantiochytrium mangrovei Using Spent Osmotic Solution from Candied Fruit Industry as Sole Organic Carbon Source

Osmotic dehydration is an important phase in the production of dried products, including most fruits and vegetables, in the food industry. The drying process for candied fruit produces a liquid waste called “spent osmotic solution”, which is characterized by a high content of organic compounds, mostly dissolved sugars. The sugar content of this food by-product could be valorized through the growth of biomass with a high added value. In this study, the spent osmotic solution from the candied fruit industry was used as an organic carbon source for the growth and production of docosahexaenoic acid (DHA) in the cultivation of Aurantiochytrium mangrovei RCC893. The carbon content of the standard media was completely replaced by the sugars present in this food by-product. After that, the growth condition of this strain was optimized through response surface methodologies using a central composite design (CCD), and the optimal combination of the spent osmotic solution and nitrogen was established. Moreover, a scale-up trial was performed using the optimal conditions obtained after CCD to evaluate the scalability of the process.

Isolation and Optimization of Culture Conditions of Thraustochytrium kinnei for Biomass Production, Nanoparticle Synthesis, Antioxidant and Antimicrobial Activities

This work deals with the identification of a predominant thraustochytrid strain, the optimization of culture conditions, the synthesis of nanoparticles, and the evaluation of antioxidant and antimicrobial activities in biomass extracts and nanoparticles. Thraustochytrium kinnei was identified as a predominant strain from decomposing mangrove leaves, and its culture conditions were optimized for maximum biomass production of 13.53 g·L−1, with total lipids of 41.33% and DHA of 39.16% of total fatty acids. Furthermore, the strain was shown to synthesize gold and silver nanoparticles in the size ranges of 10–85 nm and 5–90 nm, respectively. Silver nanoparticles exhibited higher total antioxidant and DPPH activities than gold nanoparticles and methanol extract of the strain. The silver nanoparticles showed higher antimicrobial activity than gold nanoparticles and petroleum ether extract of the strain. Thus, Thraustochytrium kinnei is proven to be promising for synthesis of silver nanoparticles with high antioxidant and antimicrobial activity.

Improvement of fatty acid productivity of thraustochytrid, Aurantiochytrium sp. by genome editing

Thraustochytrid strains belonging to the genus Aurantiochytrium accumulate significant amounts of lipids including polyunsaturated fatty acids and carotenoids and, therefore, are expected to be used for industrial production of various valuable materials. Although various efforts such as chemical mutagenesis and homologous gene recombination have been made to improve lipid productivity of Aurantiochytrium species, low specificity and efficiency in the conventional methods hinder the research progress. Here, we attempted to apply a genome editing technology, the CRISPR-Cas9 system as an alternative molecular breeding technique for Aurantiochytrium species to accelerate the metabolic engineering. The efficiency of specific gene knock-in by the homologous recombination increased more than 10-folds by combining the CRISPR-Cas9 system. As a result of disrupting the genes associated with β-oxidation of fatty acids by the improved method, the genome edited strains with higher fatty acid productivity were isolated, demonstrating for the first time that the CRISPR-Cas9 system was effective for molecular breeding of the strains in the genus Aurantiochytrium to improve lipid productivity.

Separation and purification of fatty acids by membrane technology: a critical review

Fatty acids (FAs) are a very important group of raw materials for chemical industry, and the technology of separating or purifying the FAs from the reaction product mixture has always been the hotspot of research. Membrane processes for separation of FAs are being increasingly reported. Compared with conventional FAs separation methods, membrane separation has the advantages of low energy consumption, system compactness, high separation efficiency, easy scale-up, high available surface area per unit volume and low working temperatures, thereby attracting considerable attention of many researchers. In this regards, this paper critically reviewed the developments of methods for FAs separation and purification, and the future prospects of coupling membrane technology with hydrolysis for enhanced production of FAs.

Co-production of DHA and squalene by thraustochytrid from forest biomass

Omega-3 fatty acids, and specifically docosahexaenoic acid (DHA), are important and essential nutrients for human health. Thraustochytrids are recognised as commercial strains for nutraceuticals production, they are group of marine oleaginous microorganisms capable of co-synthesis of DHA and other valuable carotenoids in their cellular compartment. The present study sought to optimize DHA and squalene production by the thraustochytrid Schizochytrium limacinum SR21. The highest biomass yield (0.46 g/g_substrate) and lipid productivity (0.239 g/g_substrate) were observed with 60 g/L of glucose, following cultivation in a bioreactor, with the DHA content to be 67.76% w/w_{total lipids}. To reduce costs, cheaper feedstocks and simultaneous production of various value-added products for pharmaceutical or energy use should be attempted. To this end, we replaced pure glucose with organosolv-pretreated spruce hydrolysate and assessed the simultaneous production of DHA and squalene from S. limacinum SR21. After the 72 h of cultivation period in bioreactor, the maximum DHA content was observed to 66.72% w/w_{total lipids} that was corresponded to 10.15 g/L of DHA concentration. While the highest DHA productivity was 3.38 ± 0.27 g/L/d and squalene reached a total of 933.72 ± 6.53 mg/L (16.34 ± 1.81 mg/g_CDW). In summary, we show that the co-production of DHA and squalene makes S. limacinum SR21 appropriate strain for commercial-scale production of nutraceuticals.

Lipid Distribution Pattern and Transcriptomic Insights Revealed the Potential Mechanism of Docosahexaenoic Acid Traffics in Schizochytrium sp. A-2

Schizochytrium sp. A-2 is a heterotrophic marine fungus used for the commercial production of docosahexaenoic acid (DHA). However, the pattern of the distribution of DHA and how DHA is channeled into phospholipid (PL) and triacylglycerol (TAG) are unknown. In this study, we systematically analyzed the distribution of DHA in TAG and PL during the growth of the cell. The migration of DHA from PL to TAG was presumed during the fermentation cycle. DHA and docosapentaenoic acid were accumulated in both TAG and phosphatidylcholine (PC), whereas eicosapentaenoic acid was mainly deposited in PC. RNA seq revealed that malic enzyme may provide lipogenic NADPH. In addition, long-chain acyl-CoA synthase and acyl-CoA:lysophosphatidylcholine acyltransferase may participate in the accumulation of DHA in PL. No phosphatidylcholine:diacylglycerol cholinephosphotransferase was identified from the genome sequence. In contrast, phospholipid:diacylglycerol acyltransferase-mediated acyl-CoA-independent TAG synthesis pathway and phospholipase C may contribute to the channeling of DHA from PC to TAG.

Nutritional intake of Aplanochytrium (Labyrinthulea, Stramenopiles) from living diatoms revealed by culture experiments suggesting the new prey-predator interactions in the grazing food web of the marine ecosystem

Labyrinthuleans (Labyrinthulea, Stramenopiles) are recognized as decomposers in marine ecosystems but their nutrient sources are not fully understood. We conducted two-membered culture experiments with labyrinthuleans and diatoms to discover where labyrinthuleans obtain their nutrients from. The results showed that Aplanochytrium strains obtained nutrients by consuming living diatoms. Aplanochytrium cells did not release digestive enzymes into the medium, but adhered to diatom cells via the tip of their characteristic ectoplasmic net system to obtain nutrients from them. The chloroplast and cell contents of the diatoms shrank and were absorbed, and then the number of Aplanochytrium cells rapidly increased as multiple aplanospores were released. To estimate the effect of labyrinthulean organisms including Aplanochytrium on marine ecosystem, we explored the dataset generated by the Tara Oceans Project from a wide range of oceanic regions. The average proportion of all labyrinthulean sequences to diatom sequences at each station was about 10%, and labyrinthulids, oblongichytrids, and aplanochytrids were the major constituent genera, accounting for more than 80% of labyrinthuleans. Therefore, these groups are suggested to greatly affect the marine ecosystem. There were positive correlations between aplanochytrids and phototrophs, green algae, and diatoms. At many stations, relatively large proportions of aplanochytrid sequences were detected in the size fraction larger than their cell size. This implied that Aplanochytrium cells increased their particle size by adhering to each other and forming aggregates with diatoms that are captured by larger zooplankton in the environment, thereby bypassing the food web pathway via aplanochytrids to higher predators. The intake of nutrients from diatoms by aplanochytrids represents a newly recognized pathway in the grazing food chain in the marine ecosystem.

Simultaneous production of DHA and squalene from Aurantiochytrium sp. grown on forest biomass hydrolysates

BACKGROUND

Recent evidence points to the nutritional importance of docosahexaenoic acid (DHA) in the human diet. Thraustochytrids are heterotrophic marine oleaginous microorganisms capable of synthesizing high amounts of DHA, as well as other nutraceutical compounds such as squalene, in their cellular compartment. Squalene is a natural triterpene and an important biosynthetic precursor to all human steroids. It has a wide range of applications in the cosmetic and pharmaceutical industries, with benefits that include boosting immunity and antioxidant activity. Apart from its nutritional quality, it can also be utilized for high-grade bio-jet fuel by catalytic conversion.

RESULTS

In the present study, the potential of thraustochytrid strain Aurantiochytrium sp. T66 to produce DHA and squalene was evaluated. When the strain was cultivated on organosolv-pretreated birch hydrolysate (30 g/L glucose) in flask, it resulted in 10.39 g/L of cell dry weight and 4.98 g/L of total lipids, of which 25.98% was DHA. In contrast, when the strain was grown in a bioreactor, cell dry weight, total lipid, and DHA increased to 11.24 g/L, 5.90 g/L, and 35.76%, respectively. The maximum squalene yield was 69.31 mg/g_CDW (0.72 g/L) when the strain was cultivated in flask, but it increased to 88.47 mg/g_CDW (1.0 g/L), when cultivation shifted to a bioreactor.

CONCLUSIONS

This is the first report demonstrating the utilization of low cost non-edible lignocellulosic feedstock to cultivate the marine oleaginous microorganism Aurantiochytrium sp. for the production of nutraceutical vital compounds. Owing to the simultaneous generation of DHA and squalene, the strain is suitable for industrial-scale production of nutraceuticals.

A New Primer Set to Amplify the Mitochondrial Cytochrome C Oxidase Subunit I (COI) Gene in the DHA-Rich Microalgae, the Genus Aurantiochytrium

This study was performed in order to develop a primer set for mitochondrial cytochrome c oxidase subunit I (COI) in the DHA-rich microalgae of the genus Aurantiochytrium. The performance of the primer set was tested using 12 Aurantiochytrium strains and other thraustochytrid species. There were no genetic polymorphisms in the mitochondrial sequences from the Aurantiochytrium strains, in contrast to the nuclear 18S rRNA gene sequence. This newly developed primer set amplified sequences from Aurantiochytrium and closely related genera, and may be useful for species identification and clarifying the genetic diversity of Aurantiochytrium in the field.

Screening of chemical modulators for lipid accumulation in Schizochytrium sp. S31

Schizochytrium sp. is a promising candidate for docosahexaenoic acid (DHA) production due to its high content of lipid and DHA proportions. To further enhance the lipid accumulation, seven chemical modulators were screened to evaluate their roles on lipid accumulation. Notably, among the seven tested chemical modulators, the addition of naphthoxyacetic acid (BNOA) or jasmonic acid (JA) was able to increase the lipid accumulation of Schizochytrium sp. S31. In addition, the effects of BNOA and JA were demonstrated dose-dependent and time-dependent, achieving a highest increase in lipid content by 11.16% and 12.71% when 2.0 mg/L of BNOA or 20 mg/L of JA was added into culture at 48 h after inoculation, respectively. In addition, the combination of 2 mg/L BNOA and 20 mg/L JA further increased lipid accumulation up to 16.79%. These results provided valuable strategy on promoting the lipid accumulation and DHA production by chemical modulators in Schizochytrium sp. S31.

Isolation and molecular characterization of Thraustochytrium strain isolated from Antarctic Peninsula and its biotechnological potential in the production of fatty acids

Thraustochytrids are unicellular protists belonging to the Labyrinthulomycetes class, which are characterized by the presence of a high lipid content that could replace conventional fatty acids. They show a wide geographic distribution, however their diversity in the Antarctic Region is rather scarce. The analysis based on the complete sequence of 18S rRNA gene showed that strain 34-2 belongs to the species Thraustochytrium kinnei, with 99% identity. The total lipid profile shows a wide range of saturated fatty acids with abundance of palmitic acid (16:0), showing a range of 16.1-19.7%. On the other hand, long-chain polyunsaturated fatty acids, mainly docosahexaenoic acid and eicosapentaenoic acid are present in a range of 24-48% and 6.1-9.3%, respectively. All factors analyzed in cells (biomass, carbon consumption and lipid content) changed with variations of culture temperature (10°C and 25°C). The growth in glucose at a temperature of 10°C presented the most favorable conditions to produce omega-3fatty acid. This research provides the identification and characterization of a Thraustochytrids strain, with a total lipid content that presents potential applications in the production of nutritional supplements and as well biofuels.

Improvement of docosahexaenoic acid fermentation from Schizochytrium sp. AB-610 by staged pH control based on cell morphological changes

Schizochytrium sp. AB-610 accumulates relatively higher amount of DHA-rich lipid in the cells, and it was found that DHA yield was closely related to the cell morphology and pH value during fermentation period. DHA production from Schizochytrium sp. AB-610 in fed-batch fermentation was investigated and four growth stages were clarified as lag stage, balanced growth stage, lipid accumulation stage, and lipid turnover stage, based on the morphologic observation and key parameters changes. Then a simple strategy of two-stage pH control was developed, in which pH 7.0 was kept until 12 h after the end of balanced growth stage, and then shifted to 5.0 for the rest period in fermentation. A maximal DHA production of 11.44g/L was achieved. This approach has advantage of easy scaling up for industrial DHA fermentation from Schizochytrium sp. cells.

Bioconversion of Docosapentaenoic Acid in Human Cell Lines, Caco-2, HepG2, and THP-1

Docosapentaenoic acids (DPAs) are long chain polyunsaturated fatty acids that exist as two major structural isomers: n-3 DPA and n-6 DPA. n-3 DPA is found in seal meat, salmon and abalone, and n-6 DPA is found in several marine microbial oil. We investigated the bioconversion of n-3 and n-6 DPAs in three different human cell lines, Caco-2, HepG2, and THP-1. n-3 DPA was converted to docosahexaenoic acid only in HepG2 cells. In contrast, retro-conversion to eicosapentaenoic acid (EPA) was observed in all three cell lines. n-6 DPA was also retro-converted to arachidonic acid (AA) in Caco-2 and HepG2 cells. EPA and AA were particularly elevated in Caco-2 cells, compared to HepG2 cells. Further, the retro-conversion of n-3 DPA led to a greater increase of EPA in the phospholipid fraction than in the neutral lipid fraction.

Genome Sequence of Schizochytrium sp. CCTCC M209059, an Effective Producer of Docosahexaenoic Acid-Rich Lipids

Schizochytrium is an effective species for producing omega-3 docosahexaenoic acid (DHA). Here, we report a genome sequence of Schizochytrium sp. CCTCC M209059, which has a genome size of 39.09 Mb. It will provide the genomic basis for further insights into the metabolic and regulatory mechanisms underlying the DHA formation.

Ecological Dynamics of Two Distinct Viruses Infecting Marine Eukaryotic Decomposer Thraustochytrids (Labyrinthulomycetes, Stramenopiles)

Thraustochytrids are cosmopolitan osmotrophic or heterotrophic microorganisms that are considered as important decomposers in coastal ecosystems. However, because of a lack of estimation method for each genus or systematic group of them, relatively little is known about their ecology in situ. Previously, we reported two distinct types of virus infecting thraustochytrids (AuRNAV: reported as SssRNAV, and SmDNAV) suggesting they have wide distributions in the host-virus systems of coastal environments. Here we conducted a field survey from 2004 through 2005 to show the fluctuation pattern of thraustochytrids and their viruses in Hiroshima Bay, Japan. During the field survey, we monitored the dynamics of the two types of thraustochytrid-infecting virus: small viruses causing lysis of Aurantiochytrium sp. NIBH N1-27 (identified as AuRNAV) and the large viruses of Sicyoidochytrium minutum NBRC 102975 (similar to SmDNAV in physiology and morphology). Fluctuation patterns of the two distinct types of virus were different from each other. This may reflect the difference in the preference of organic substrates; i.e., it may be likely the host of AuRNAV (Aurantiochytrium sp.) increases utilizing algal dead bodies or feeble cells as the virus shows a large increase in abundance following raphidophyte blooms; whereas, the trophic nutrient supply for S. minutum may primarily depend on other constantly-supplied organic compounds because it did not show any significant change in abundance throughout the survey. Further study concerning the population composition of thraustochytrids and their viruses may demonstrate the microbial ecology (especially concerning the detrital food web) of marine environments.

Response surface optimization of culture medium for enhanced docosahexaenoic acid production by a Malaysian thraustochytrid

Docosahexaenoic acid (DHA, C22:6n-3) plays a vital role in the enhancement of human health, particularly for cognitive, neurological, and visual functions. Marine microalgae, such as members of the genus Aurantiochytrium, are rich in DHA and represent a promising source of omega-3 fatty acids. In this study, levels of glucose, yeast extract, sodium glutamate and sea salt were optimized for enhanced lipid and DHA production by a Malaysian isolate of thraustochytrid, Aurantiochytrium sp. SW1, using response surface methodology (RSM). The optimized medium contained 60 g/L glucose, 2 g/L yeast extract, 24 g/L sodium glutamate and 6 g/L sea salt. This combination produced 17.8 g/L biomass containing 53.9% lipid (9.6 g/L) which contained 44.07% DHA (4.23 g/L). The optimized medium was used in a scale-up run, where a 5 L bench-top bioreactor was employed to verify the applicability of the medium at larger scale. This produced 24.46 g/L biomass containing 38.43% lipid (9.4 g/L), of which 47.87% was DHA (4.5 g/L). The total amount of DHA produced was 25% higher than that produced in the original medium prior to optimization. This result suggests that Aurantiochytrium sp. SW1 could be developed for industrial application as a commercial DHA-producing microorganism.

Production of high docosahexaenoic acid by Schizochytrium sp. using low-cost raw materials from food industry

The low-cost substrates from food industry, including maize starch hydrolysate and soybean meal hydrolysate, were used to produce docosahexaenoic acid (DHA) by Schizochytrium limacinum OUC88. Glucose derived from maize starch hydrolysate was used as the carbon source and soybean meal hydrolysate as the nitrogen sources. In 10L bioreactor fermentation, by using the soybean meal hydrolysate as the main nitrogen source, the biomass of Schizochytrium limacinum OUC88 reached 85.27 g L(-1), and the yields of DHA was 20.7g L(-1). As a comparison, when yeast extract was used as the main nitrogen source, the yields of biomass and DHA were 68.93 g L(-1) and 13.3 g L(-1), respectively. From the results of this study, these hydrolysates can provide all the nutrients required for high-density cultivation of S. limacinum OUC88 and DHA production, that will improve the economical and competitive efficiency of commercial DHA production.

Pollen baiting facilitates the isolation of marine thraustochytrids with potential in omega-3 and biodiesel production

Marine heterotrophic microbes are capable of accumulating large amounts of lipids, omega-3 fatty acids, carotenoids, and have potential for biodiesel production. Pollen baiting using Pinus radiata pollen grain along with direct plating techniques were used in this study as techniques for the isolation of oil-producing marine thraustochytrid species from Queenscliff, Victoria, Australia. Thirteen isolates were obtained using either direct plating or using pine pollen, with pine pollen acting as a specific substrate for the surface attachment of thraustochytrids. The isolates obtained from the pollen baiting technique showed a wide range of docosahexaenoic acid (DHA) accumulation, from 11 to 41 % of total fatty acid content (TFA). Direct plating isolates showed a moderate range of DHA accumulation, from 19 to 25 % of TFA. Seven isolates were identified on the basis of 18S rRNA sequencing technique as Thraustochytrium species, Schizochytrium species, and Ulkenia species. Although both methods appear to result in the isolation of similar strains, pollen baiting proved to be a simpler method for the isolation of these relatively slow-growing organisms.

Increase in stearidonic acid by increasing the supply of histidine to oleaginous Saccharomyces cerevisiae

Increasing concentration of histidine significantly increased stearidonic acid production and cell growth in oleaginous Saccharomyces cerevisiae that has been genetically modified by Δsnf2 disruption, DGA1 and Δ6 desaturase gene overexpression, and LEU2 expression. High concentration of histidine in wild-type transformant and HIS3 expression in Δsnf2 transformant also increased stearidonic acid.

Improving docosahexaenoic acid productivity of Schizochytrium sp. by a two-stage AEMR/shake mixed culture mode

In this work, an aeration-enhanced membrane reactor (AEMR) was built to control dissolved oxygen in Schizochytrium sp. broth. The effect of culture modes, i.e. single shake and AEMR mode, on the docosahexaenoic acid (DHA) productivity of Schizochytrium sp. was investigated. Experimental results showed that the biomass production in the AEMR mode was higher than that in the single shake mode, while the final DHA productivity in single shake mode was higher than that in the AEMR mode. A two-stage mixed culture mode was proposed, in which Schizochytrium sp. was cultured in AEMR mode at a flow rate of 0.2 L min(-1) for 60 h to first increase biomass production, and then shifted to shake mode to improve DHA productivity. Compared to the single shake mode, the DHA productivity in mixed mode costed 40% less culture time and the DHA productivity at 96 h exhibited a relative increase of 60%.

Alternative sources of n-3 long-chain polyunsaturated fatty acids in marine microalgae

The main source of n-3 long-chain polyunsaturated fatty acids (LC-PUFA) in human nutrition is currently seafood, especially oily fish. Nonetheless, due to cultural or individual preferences, convenience, geographic location, or awareness of risks associated to fatty fish consumption, the intake of fatty fish is far from supplying the recommended dietary levels. The end result observed in most western countries is not only a low supply of n-3 LC-PUFA, but also an unbalance towards the intake of n-6 fatty acids, resulting mostly from the consumption of vegetable oils. Awareness of the benefits of LC-PUFA in human health has led to the use of fish oils as food supplements. However, there is a need to explore alternatives sources of LC-PUFA, especially those of microbial origin. Microalgae species with potential to accumulate lipids in high amounts and to present elevated levels of n-3 LC-PUFA are known in marine phytoplankton. This review focuses on sources of n-3 LC-PUFA, namely eicosapentaenoic and docosahexaenoic acids, in marine microalgae, as alternatives to fish oils. Based on current literature, examples of marketed products and potentially new species for commercial exploitation are presented.

Use of organic waste from the brewery industry for high-density cultivation of the docosahexaenoic acid-rich microalga, Aurantiochytrium sp. KRS101

In the present study, spent yeast from a brewery was used as the growth substrate for the docosahexaenoic acid (DHA)-rich microalga, Aurantiochytrium sp. KRS101. A significant biomass yield (6.69 g/l/d) was obtained using only spent yeast as the growth substrate, with simple stirring as pretreatment. Maximization of nutrient utilization through the use of stepwise cultivation increased the yield to 31.8 g/l of biomass. DHA constituted 38.2% (w/w) of the total fatty acids, and the highest DHA productivity was observed when the C/N ratio was 20:1 (w/w). Spent yeast thus served as a good growth substrate for the production of DHA. Economic assessment revealed that stepwise cultivation using spent yeast as either the sole growth substrate or as a nutrient source could substantially reduce the production cost of microalgal DHA.

Effects of cold shock treatment on total lipid content and fatty acid composition of Aurantiochytrium limacinum strain mh0186

To examine the effect of cold shock treatment on the fatty acid composition of Aurantiochytrium limacinum strain mh0186, a marine thraustochytrid, we cultivated this strain at 28°C for 72 h with shaking and stored the obtained biomass at 10°C for 72 h. A growth experiment was carried out for comparison, wherein strain mh0186 was grown at 10 and 15°C for 72 h with shaking, and it was found that the unsaturation of fatty acids was accelerated relative to that at 28°C. In the cold shock experiment, the total lipid content significantly increased during storage at 10°C for 72 h. Overall, the percentage of unsaturated fatty acids such as docosahexaenoic acid was almost stable while that of n-6 docosapentaenoic acid decreased slightly, but significantly, relative to that in the growth experiment.

STUDY ON BIOLOGICAL CHARACTERISTICS OF HETEROTROPHIC MARINE MICROALGA-SCHIZOCHYTRIUM MANGROVEI PQ6 ISOLATED FROM PHU QUOC ISLAND, KIEN GIANG PROVINCE, VIETNAM(1)

Schizochytrium sp. PQ6, a heterotrophic microalga isolated from Phu Quoc (PQ) Island in the Kien Giang province of Vietnam, contains a high amount of docosahexaenoic acid (DHA, C22:6n-3). In this study, the culture conditions are developed to maximize biomass and DHA production. Nucleotide sequence analysis of partial 18S rRNA gene from genomic DNA showed that PQ6 has a phylogenetic relationship close to Schizochytrium mangrovei Raghu-Kumar. The highest growth rate and DHA accumulation of this strain were obtained in 6.0% glucose, 1.0% yeast extract, 50% artificial seawater (ASW), and pH 7 at 28°C. In addition, carbon and nitrogen sources could be replaced by glycerol, ammonium acetate, sodium nitrate, or fertilizer N-P-K. Total lipid content reached 38.67% of dry cell weight (DCW), in which DHA and eicosapentaenoic acid (EPA, C20:5n-3) contents accounted for 43.58% and 0.75% of the total fatty acid (TFA), respectively. In 5 and 10 L fermenters, the cell density, DCW, total lipid content, and maximum DHA yield were 46.50 × 10(6)  cells · mL(-1) , 23.7 g · L(-1) , 38.56% of DCW, and 8.71 g · L(-1) (in 5 L fermenter), respectively, and 49.71 × 10(6)  cells · mL(-1) , 25.34 g · L(-1) , 46.23% of DCW, and 11.55 g · L(-1) (in 10 L fermenter), respectively. Biomass of PQ6 strain possessed high contents of Na, I, and Fe (167.185, 278.3, and 43.69 mg · kg(-1) DCW, respectively). These results serve as a foundation for the efficient production of PQ6 biomass that can be used as a food supplement for humans and aquaculture in the future.

Development of a stepwise aeration control strategy for efficient docosahexaenoic acid production by Schizochytrium sp

The effect of aeration on the performance of docosahexaenoic acid (DHA) production by Schizochytrium sp. was investigated in a 1,500-L bioreactor using fed-batch fermentation. Six parameters, including specific growth rate, specific glucose consumption rate, specific lipid accumulation rate, cell yield coefficient, lipid yield coefficient, and DHA yield coefficient, were used to understand the relationship between aeration and the fermentation characteristics. Based on the information obtained from the parameters, a stepwise aeration control strategy was proposed. The aeration rate was controlled at 0.4 volume of air per volume of liquid per minute (vvm) for the first 24 h, then shifted to 0.6 vvm until 96 h, and then switched back to 0.4 vvm until the end of the fermentation. High cell density (71 g/L), high lipid content (35.75 g/L), and high DHA percentage (48.95%) were achieved by using this strategy, and DHA productivity reached 119 mg/L h, which was 11.21% over the best results obtained by constant aeration rate.

Isolation and characterization of Taiwanese heterotrophic microalgae: screening of strains for docosahexaenoic acid (DHA) production

Marine heterotrophic microalgal species which are potentially rich in docosahexaenoic acid (DHA, C22:6n-3) have been found in Taiwan; however, there was a lack of detailed analysis and characterization of these indigenous algae which is needed for the development of commercial applications. Hence, the objective of this study was to screen DHA-rich heterotrophic microalgae species indigenous to Taiwan for commercial purposes. Heterotrophic microalgae from a variety of marine habitats were isolated, cultivated, and then identified according to their 18S rRNA gene sequences and morphological characteristics. A comparison was made of their fatty acid profiles, fatty acid content, and amount of biomass. For the strain with highest DHA yield, the optimal growth conditions were determined in order to establish the best fermentation conditions for scale-up. In this study, 25 heterotrophic microalgal strains were successfully isolated from marine habitats around Taiwan. All of the isolated strains showed a close phylogenic relationship with the Thraustochytriaceae family according to their 18S rRNA gene sequences. GC/MS analysis discerned seven distinctive fatty acid profiles of these strains, with the production of eicosapentaenoic acid (C20:5n-3) ranging from 0.02 to 2.61 mg L(-1), and DHA ranging from 0.8 to 18.0 mg L(-1). An Aurantiochytrium strain BL10 with high DHA production was subsequently chosen for further manipulation. Under optimal growth conditions it could produce up to 59.0 g of dry biomass per liter of culture, with dry biomass containing 73% total fatty acid and 29% DHA, revealing BL10 as an excellent source of microbial DHA.