Docosahexaenoic Acid Yield Research Articles

Enrichment of EPA and DHA in glycerides by selective enzymatic ethanolysis

It has been reported that eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in glycerides have various biological functions. This study presents an effective method for enriching glycerides rich in EPA and DHA through lipase-catalyzed alcoholysis. The results showed that Eversa® Transform 2.0 had the strongest discrimination against DHA and EPA in alcoholysis, which was verified by molecular docking. Additionally, selectivity of the lipase and ratio of DHA and EPA in glyceride products were significantly affected by alcohol type. Under the optimal conditions, the contents of EPA and DHA in glycerides after ethanolysis reached 12.91 % and 55.40 %, respectively, with a DHA yield of 79.22 %. In this study, an interesting finding was that Eversa® Transform 2.0 could effectively differentiate EPA and DHA during alcoholysis to allow us to prepare DHA-enriched glycerides and EPA-enriched ethyl esters after removing saturated and monounsaturated ethyl esters.

Integrated production of xylose and docosahexaenoic acid from hemicellulose and cellulose in corncob

Exploring efficient and comprehensive utilization of agricultural waste to produce high value-added products has been global research hotspot. In this study, a novel process for integrated production of xylose and docosahexaenoic acid (DHA) from hemicellulose and cellulose in corncob was developed. Corncob was treated with dilute H2SO4 at 121 °C for 1 h and xylose was readily produced with a recovery yield of 79.35 %. The corncob residue was then subject to alkali pretreatment under optimized conditions of 0.1 g NaOH/g dry solid, 60 °C for 2 h, and the contents of cellulose, hemicellulose, and lignin in the resulting residue were 87.49 %, 7.58 % and 2.31 %, respectively. The cellulose in the residue was easily hydrolyzed by cellulase, yielding 74.87 g/L glucose with hydrolysis efficiency of 77.02 %. Remarkably, the corncob residue hydrolysate supported cell growth and DHA production in Schizochytrium sp. ATCC 20888 well, and the maximum biomass of 32.71 g/L and DHA yield of 4.63 g/L were obtained, with DHA percentage in total fatty acids of 36.89 %. This study demonstrates that the corncob residue generated during xylose production, rich in cellulose, can be effectively utilized for DHA production by Schizochytrium sp., offering a cost-effective and sustainable alternative to pure glucose.

Selectively superior production of docosahexaenoic acid in Schizochytrium sp. through engineering the fatty acid biosynthetic pathways

BackgroundSchizochytrium sp. is commercially used for production of docosahexaenoic acid (DHA). Schizochytrium sp. utilizes the polyketide synthase complex (PKS) and a single type I fatty acid synthase (FAS) to synthesize polyunsaturated fatty acids and saturated fatty acids, respectively. The acyl carrier protein (ACP) domains of FAS or PKS are used to load acyl groups during fatty acids biosynthesis. Phosphopantetheinyl transferase (PPTase) transfers the pantetheine moiety from Coenzyme A to the conserved serine residue of an inactive ACP domain to produce its active form.ResultsIn this study, in order to improve production and content of DHA, we decreased the expression of fas, strengthened the expression of the PKS pathway, and enhanced the supply of active ACP in Schizochytrium sp. ATCC20888. Weakening the expression of fas or disruption of orfA both led to growth defect and reduction of lipid yields in the resulting strains WFAS and DPKSA, indicating that both FAS and PKS were indispensable for growth and lipid accumulation. Although WFAS had a higher DHA content in total fatty acids than the wild-type strain (WT), its growth defect and low DHA yield hinders its use for DHA production. Overexpression of the orfAB, orfC, orfC-DH (truncated orfC), or ppt promoted DHA and lipid production, respectively. The yields and contents of DHA were further increased by combined overexpression of these genes. Highest values of DHA yield (7.2 g/L) and DHA content (40.6%) were achieved in a recombinant OPKSABC-PPT, ⁓56.5% and 15.3% higher than the WT values, respectively.ConclusionsThis study demonstrates that genetic engineering of the fatty acid biosynthetic pathways provides a new strategy to enhance DHA production in Schizochytrium.

Concentration-dependent dual roles of proanthocyanidins on oxidative stress and docosahexaenoic acid production in Schizochytrium sp. ATCC 20888

Antioxidant addition is an effective strategy to achieve docosahexaenoic acid (DHA) overproduction in oleaginous microorganisms. Nevertheless, antioxidants like phenolic compounds sometimes exert pro-oxidant activity. In this work, effects of proanthocyanidins (PAs) on fermentation performance and oxidative stress in Schizochytrium sp. were investigated. Low PAs addition (5 mg/L) reduced reactive oxygen species and enhanced lipogenic enzymes activities and NADPH, resulting in significant increase in lipid (20.3 g/L) by 33.6 % and DHA yield (9.8 g/L) by 53.4 %. In contrast, high PAs addition (500 mg/L) exerted pro-oxidant effects, aggravated oxidative damage and lipid peroxidation, leading to sharp decrease in biomass (21.3 g/L) by 35.1 %, lipid (8.2 g/L) by 46.0 %, and DHA (2.9 g/L) by 54.8 %. Therefore, the antioxidant concentration is especially crucial in DHA production. This study is the first to report concentration-dependant dual roles of PAs in oxidative stress and DHA production in Schizochytrium sp., providing new insights into microbial DHA production.

Genetic Modification of Aurantiochytrium sp. 18W-13a for Enhancement of Proteolytic Activity by Heterologous Expression of Extracellular Proteases.

A marine thraustochytrid, Aurantiochytrium, is a promising organism to produce docosahexaenoic acid (DHA) and squalene. Utilization of inexpensive substances such as proteins in wastes and by-products from the food industry for cultivation is a considerable option to reduce production cost; however, the proteolytic ability of Aurantiochytrium spp. is low compared to taxonomically close Shizochytrium aggregatum. We previously identified extracellular protease (extracellular protease 1, EP1) in S. aggregatum ATCC 28209 from the supernatant of the culture and found that a similar protease gene (EP2) was located downstream of the EP1 gene. In the present study, we created the transformants expressing SaEP1 and/or SaEP2 to enhance the proteolytic ability of Aurantiochytrium sp. 18W-13a strain and cultivated them in the medium containing casein as a test protein substrate. Through SDS-PAGE analysis, we confirmed that casein in the supernatant was more efficiently degraded by the transformants than the wild type, suggesting that the expressed protease(s) were properly expressed and excreted. After 4-day cultivation in the casein medium, the value of optical density at 660nm and the cell number in the culture of the transformant that expressed both SaEP1 and SaEP2 (designated as EP12 strain) showed 1.48- and 1.38-fold higher than those of wild type, respectively. The DHA and squalene yield of the EP12 strain were respectively 158.3 and 0.23mg L-1, and these values were 1.42- and 2.01-fold higher than those of wild type, respectively, suggesting that the EP12 created in the present study is a favorable strain for the cultivation using protein-containing medium.

Extraction, separation and purification of fatty acid ethyl esters for biodiesel and DHA from Thraustochytrid biomass.

A novel approach for in situ transesterification, extraction, separation, and purification of fatty acid ethyl esters (FAEE) for biodiesel and docosahexaenoic acid (DHA) from Thraustochytrid biomass has been developed. The downstream processing of Thraustochytrids oil necessitates optimization, considering the higher content of polyunsaturated fatty acids (PUFA). While two-step methods are commonly employed for extracting and transesterifying oil from oleaginous microbes, this may result in oxidation/epoxidation of omega-3 oil due to prolonged exposure to heat and oxygen. To address this issue, a rapid single-step method was devised for in situ transesterification of Thraustochytrid oil. Through further process optimization, a 50% reduction in solvent requirement was achieved without significantly impacting fatty acid recovery or composition. Scale-up studies in a 4L reactor demonstrated complete FAEE recovery (99.98% of total oil) from biomass, concurrently enhancing DHA yield from 16% to nearly 22%. The decolorization of FAEE oil with fuller's earth effectively removed impurities such as pigments, secondary metabolites, and waxes, resulting in a clear, shiny appearance. High-performance liquid chromatography (HPLC) analysis indicated that the eluted DHA was over 94.5% pure, as corroborated by GC-FID analysis.

Enhancing docosahexaenoic acid production in Aurantiochytrium species using atmospheric and room temperature plasma mutagenesis and comprehensive multi-omics analysis

Aurantiochytrium sp. belongs to marine heterotrophic single-cell protist, which is an important decomposer in marine ecosystem. Aurantiochytrium sp. has gained notoriety because of its ability to accumulate high-value docosahexaenoic acid (DHA), but the key factors of DHA synthesis were unclear at present. In this study, Atmospheric and Room Temperature Plasma technology was applied to the mutagenic breeding of Aurantiochytrium sp., and transcriptomics and proteomics were adopted to analyze the DHA-biosynthesis mechanism. According to the growth and DHA accumulation profiles, the mutant strain Aurantiochytrium sp. R2A35 was selected. The DHA content in total lipids was greatly improved from 49.39 % of the wild strain R2 to 63.69 % of the mutant strain. Moreover, the DHA content in the biomass of Aurantiochytrium sp. R2A35 as 39.72 % was the highest DHA productivity reported so far. The differentially expressed genes distinguished from transcriptome and the TMT-identified differential proteins distinguished from proteome confirmed that the expression of acetyl-CoA carboxylase and ketoacyl reductase was up-regulated by 4.78-fold and 6.95-fold, respectively and the fatty acid synthase was concurrently down-regulated by 2.79-fold, so that more precursor was transported to the polyketide synthase pathway, thereby increasing the DHA yield in Aurantiochytrium sp. R2A35. This research would provide reference for the DHA metabolism process and contribute to the understanding of the decomposer - Aurantiochytrium sp. in marine ecosystems.

Metabolic engineering of Schizochytrium sp. for superior docosahexaenoic acid production

Schizochytrium sp. is an industrial producer of docosahexaenoic acid (DHA), which is an important omega-3 polyunsaturated fatty acid used in the nutraceutical and food industry. Here, we rewired the carbon metabolism of Schizochytrium sp. ATCC20888 for superior DHA production and constructed 18 engineered strains through combinatorial gene manipulation of 8 crucial genes (acc, acl, ampD, dga1, mae, mfe1, pex10, and zwf) related to lipogenesis. Reducing β-oxidations (∆pex10, ∆mfe1), reinforcing the biosynthetic precursors supply (OACC, OACL, OAMPD), reinforcing NADPH supply (OMAE, OZWF), or promoting TAG formation (ODGA1) efficiently promoted DHA and lipid production of Schizochytrium. MAE and DGA1 overexpression exhibited cooperativity towards increasing DHA production and lipogenesis in the WT strain and ACC-overexpression strain, but had no cooperative advantage in the ∆pex10 strain. The highest lipid content (82.2%) and DHA yield (7.04 g/L) were obtained in an engineered strain OACL-ACC/∆pex10, which is 72.1% higher than DHA yield of parental strain. Therefore, inhibition of β-oxidations and ample biosynthetic precursors supply are the determining factors for high DHA productivity and lipid accumulation of Schizochytrium.

Development of a green fermentation strategy with resource cycle for the docosahexaenoic acid production by Schizochytrium sp.

The fermentation production of docosahexaenoic acid (DHA) is an industrial process with huge consumption of freshwater resource and nutrient, such as carbon sources and nitrogen sources. In this study, seawater and fermentation wastewater were introduced into the fermentation production of DHA, which could solve the problem of fermentation industry competing with humans for freshwater. In addition, a green fermentation strategy with pH control using waste ammonia, NaOH and citric acid as well as FW recycling was proposed. It could provide a stable external environment for cell growth and lipid synthesis while alleviating the dependence on organic nitrogen sources of Schizochytrium sp. It was proved that this strategy has good industrialization potential for DHA production, and the biomass, lipid and DHA yield reached to 195.8 g/L, 74.4 g/L and 46.4 g/L in 50 L bioreactor, respectively. This study provides a green and economic bioprocess technology for DHA production by Schizochytrium sp.

Bioprocess engineering to produce essential polyunsaturated fatty acids from Thraustochytrium sp.

In recent studies, thraustochytrid has emerged as a sustainable substitute to fish oil or polyunsaturated fatty acid (PUFA) sources: docosapentaenoic acid (DPA) eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). Due to growing health concerns, there is increasing demand for food and health applications of PUFA for several diseases, aquaculture feeds, and dietary products. Thraustochytrium sp. found a sustainable source for considerable PUFA and SFA production and to meet omega PUFA demand globally. This study aims to increase PUFA yield by the maximum possible glucose carbon with an appropriate nitrogen ratio (10:1). The maximum biomass and lipid obtained from 40 g/L glucose, were 7.47 ± 0.3 g/L and 4.63 g/L (60.84 ± 1.4%), respectively. However, maximum relative lipid, DHA and DPA yields were from 30 g/L glucose i.e, 67.6 ± 1.9 % and 963.58 ± 24 and 693.10 ± 24 mg/L respectively with complete glucose assimilation. Thus, this could be a potential source of commercial DPA and DHA producers under the biorefinery scheme.

Menthol‐based deep eutectic solvents as green extractants for the isolation of omega‐3 polyunsaturated fatty acids from Perna canaliculus

AbstractBACKGROUNDMarine‐derived omega‐3 polyunsaturated fatty acids (PUFA) are used globally as food supplements for their anti‐inflammatory properties and to reduce the risk of obesity, cardiovascular diseases, and cancer. New Zealand green‐lipped mussels (Perna canaliculus) contain diverse valuable compounds, including omega‐3 PUFA. The most abundant omega‐3 PUFA in Perna canaliculus are eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), both of which account for many of the health benefits accredited to these mussels. This research investigates the feasibility of using deep eutectic solvents (DESs) to isolate EPA and DHA from Perna canaliculus.RESULTSTwenty‐two hydrophobic DESs were screened using COSMO‐RS software to predict their affinity for EPA and DHA. Nine top‐ranked DESs were used for experimental extraction validation. The results exposed that the extraction capacity of the menthol: lidocaine DES (1:1 M ratio) for EPA and DHA was superior (172.04 μg EPA g−1 dry weight (DW) of biomass and 602.79 μg DHA g−1 DW) amongst other DESs. This was a considerably higher extraction yield than that observed using ethanol (95.65 μg EPA g−1 DW and 311.49 μg DHA g−1 DW). The optimisation of the menthol: lidocaine ratio identified a 1:2 M ratio as the optimal composition for this DES. The highest yields of EPA (267.59 μg g−1 DW) and DHA (1014.84 μg g−1 DW) were obtained by this optimised DES ratio at optimum extraction conditions (extraction temperature 65 °C, extraction time 2.12 h, and biomass loading 5 w/v%). The EPA and DHA showed good stability in the menthol: lidocaine DES over 7 days. This DES also showed good reusability, with a comparable extraction efficiency being observed after five extraction cycles.CONCLUSIONThis research revealed that menthol‐based DES can be a potential green solvent for the extraction of EPA and DHA from New Zealand green‐lipped mussels and it may be applicable for extracting other bioactive compounds with similar characteristics. © 2023 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).

Enhancing Docosahexaenoic Acid Production of Isochrysis galbana from Starch-Rich Food Processing Byproducts

Leftover dough, a byproduct in steamed bread processing, is rich in starch, which is a carbohydrate source for microorganisms. Carbon and nitrogen are the two most abundant nutrients in the medium of Isochrysis galbana. In this study, the leftover dough hydrolysates were used as carbon resources for the cultivation of Isochrysis galbana for docosahexaenoic acid production under different NaNO3 concentrations. The results showed that hydrolysates and NaNO3 concentration affected cell growth and docosahexaenoic acid (DHA) accumulation significantly. The maximum biomass concentration of 4.18 g L−1 and maximum DHA yield of 341.3 mg L−1 were obtained with 50.0 mL L−1 hydrolysates. The DHA yield of Isochrysis galbana with 300.0 mg L−1 NaNO3 was 8.9-fold higher than that of the control. The results showed that the DHA production of Isochrysis galbana from starch-rich food processing byproducts was enhanced.

Construction of Glucose-6-Phosphate Dehydrogenase Overexpression Strain of Schizochytrium sp. H016 to Improve Docosahexaenoic Acid Production.

Docosahexaenoic acid (DHA) is an important omega-3 polyunsaturated fatty acid (PUFA) that plays a critical physiological role in human health. Schizochytrium sp. is considered an excellent strain for DHA production, but the synthesis of DHA is limited by the availability of nicotinamide adenine dinucleotide phosphate (NADPH). In this study, the endogenous glucose-6-phosphate dehydrogenase (G6PD) gene was overexpressed in Schizochytrium sp. H016. Results demonstrated that G6PD overexpression increased the availability of NADPH, which ultimately altered the fatty acid profile, resulting in a 1.91-fold increase in DHA yield (8.81 g/L) and increased carbon flux by shifting it from carbohydrate and protein synthesis to lipid production. Thus, G6PD played a vital role in primary metabolism. In addition, G6PD significantly increased DHA content and lipid accumulation by 31.47% and 40.29%, respectively. The fed-batch fermentation experiment results showed that DHA production reached 17.01 g/L in the overexpressing G6PD strain. These results elucidated the beneficial effects of NADPH on the synthesis of PUFA in Schizochytrium sp. H016, which may be a potential target for metabolic engineering. Furthermore, this study provides a promising regulatory strategy for the large-scale production of DHA in Schizochytrium sp.

Enhancing docosahexaenoic acid production of Schizochytrium sp. by optimizing fermentation using central composite design.

Docosahexaenoic acid (DHA) can improve human and animal health, particularly including anti-inflammatory, antioxidant, anticancer, neurological, and visual functions. Schizochytrium sp. is a marine heterotrophic protist producing oil with high DHA content, which is widely used in animal and food production. However, different fermentation conditions have intensive impacts on the growth and DHA content of Schizochytrium sp. Thus, this study aimed to enhance the DHA yield and concentration of Schizochytrium sp. I-F-9 by optimizing the fermentation medium. First, a single-factor design was conducted to select a target carbon and nitrogen source from several generic sources (glucose, sucrose, glycerol, maltose, corn syrup, yeast extract, urea, peptone, and ammonium sulfate). The Plackett-Burman design and the central composite design (CCD) were utilized to optimize the fermentation mediums. Schizochytrium sp. in 50-mL fermentation broth was cultured in a 250mL shake flask at 28°C and 200rpm for 120h before collecting the cell pellet. Subsequently, the cell walls were destroyed with hydrochloric acid to extract the fatty acid using n-hexane. The DHA content was detected by gas chromatography. The single-factor test indicated that glucose and peptone, respectively, significantly improved the DHA content of Schizochytrium sp. compared to the other carbon and nitrogen sources. Glucose, sodium glutamate, and sea crystal were the key factors affecting DHA production in the Plackett-Burman test (P = 0.0247). The CCD result showed that DHA production was elevated by 34.73% compared with the initial yield (from 6.18 ± 0.063 to 8.33 ± 0.052g/L). Therefore, the results of this study demonstrated an efficient strategy to increase the yield and content of DHA of Schizochytrium sp.

Yacon (Smallanthus sonchifolius) tuber: A novel and promising feedstock for enhanced high-value docosahexaenoic acid production by Schizochytrium sp.

Fermentation cost and oxygen-mediated lipid peroxidation have become economic and technical bottlenecks for the commercialization of docosahexaenoic acid (DHA) from microorganisms. Yacon (Smallanthus sonchifolius) tuber is rich in fructan, phenolics and other nutrients, and it represents a low-cost and abundant feedstock for microbial fermentation. Herein, yacon tuber hydrolysate (YTH) yielded by exo-inulinase was used as a novel potential substrate for Schizochytrium sp. ATCC 20888 to produce DHA. Under the optimized medium composition of reducing sugar of 100 g/L, C/N ratio of 30 and C/P ratio of 200, the maximal biomass, lipid and DHA yield in YTH medium reached 50.60, 24.44 and 10.85 g/L, respectively, which were much higher than those produced with glucose and fructose. Antioxidant capacity and enzyme activity analysis showed that the superior fermentation performance using YTH was mainly attributed to the significant increase in the activities of related key lipogenic enzymes, the reduction in intracellular reactive oxygen species and the inhibition of lipid peroxidation. Therefore, yacon tuber was proven to be an ideal alternative feedstock for efficient high-value DHA production by Schizochytrium sp.

Comparative transcriptomic and lipidomic analyses indicate that cold stress enhanced the production of the long C18-C22 polyunsaturated fatty acids in Aurantiochytrium sp.

Aurantiochytrium sp. belonging to Thraustochytrids are known for their capacity to produce long-chain polyunsaturated fatty acids (PUFAs). However, effects of cold stress accompanied with staged-temperature control on the fatty acid metabolism in Aurantiochytrium sp. were rarely studied. In this study, cold stress (15°C, 5°C) was applied for Aurantiochytrium sp., with the physiological responses (morphology, growth, fatty acid profiling) and gene expression related FA synthesis, lipid metabolism, and regulatory processes was observed. Results showed that there is a significant change for the lipid types under 5°C (251 species) and 15°C (97 species) treatment. The 5°C treatment was benefit for the C18–C22 PUFAs with the yield of docosahexaenoic acid (DHA) increased to 1.25 times. After incubation at 15°C, the accumulation of eicosadienoic acid (EA) (20:2) was increased to 2.00-fold. Based on transcriptomic and qPCR analysis, an increase in genes involved in fatty acid synthase (FAS) and polyketide synthase (PKS) pathways was observed under low-temperature treatment. With upregulation of 3-ketoacyl-CoA synthase (2.44-fold), ketoreductase (2.50-fold), and dTDP-glucose 4,6-Dehydratase (rfbB) (2.31-fold) involved in PKS pathway, the accumulation of DHA was enhanced under 5°C. While, FAS and fatty elongase 3 (ELO) involved in the FAS pathway were upregulated (1.55-fold and 2.45-fold, respectively) to accumulate PUFAs at 15°C. Additionally, glycerol-3-phosphate acyltransferase (GPAT), lysophospholipid acyltransferase (LPAT), phosphatidic acid phosphatase (PAP), phosphatidylserine synthase (PSS), and phosphatidylserine decarboxylase (PSD) involved in glycerophospholipid biosynthesis were upregulated at 5°C increasing the accumulation of phosphatidic acid (PA), phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylglycerol (PG), and phosphatidylinositol (PI). However, glycolysis and the TCA cycle were inhibited under 5°C. This study provides a contribution to the application of two-staged temperature control in the Aurantiochytrium sp. fermentation for producing cold stress-enhancing PUFAs, in order to better understand the function of the key genes for future genetic engineering.

Transcriptome analyses reveal the DHA enhancement mechanism in Schizochytrium limacinum LD11 mutant

Schizochytrium is the main strain used for the industrial production of docosahexaenoic acid (DHA), and improving its yield is a constant requirement in the industry. A mutant of Schizochytrium limacinum LD11 with high DHA production was screened through atmospheric and room temperature plasma (ARTP) mutations using S. limacinum B4D1 as parent strain. A comparative transcriptome was used to reveal the DHA production enhancement mechanism of LD11 by comparing with B4D1. The DHA yield of LD11 reached 14.27 g/L, which was 25.51 % higher than that of B4D1. Transcriptome analysis revealed that genes involved in the tricarboxylic acid cycle and citrate transport system were significantly upregulated in LD11 compared with B4D1, providing more acetyl-CoA for the synthesis of fatty acids. Additionally, the triacylglycerol synthesis pathway was upregulated. Genes involved in β-oxidation in mitochondria and peroxisomes were upregulated and downregulated, respectively, resulting in a significant increase in the content of DHA. This study provides an efficient breeding strategy to improve DHA production in Schizochytrium, and it shows that transcriptome results can be used as a basis for metabolic engineering. • Schizochytrium limacinum LD11 with high DHA production was screened. • Comparative transcriptome was conducted to reveal the mutant mechanism. • Genes from TCA, citrate transport system were significantly up-regulated in LD11. Genes involved in β-oxidation in mitochondria were up-regulated in LD11. • Genes involved in peroxisomes were down-regulated in LD11.

Docosahexaenoic acid production of the marine microalga Isochrysis galbana cultivated on renewable substrates from food processing waste under CO2 enrichment

Leftover dough is a starch-rich food processing waste of Chinese steamed bread. Leftover dough hydrolysates enriched with glucose and amino acids were used to cultivate the marine microalga Isochrysis galbana to produce docosahexaenoic acid (DHA) under CO2 enrichment. Isochrysis galbana could use mixed carbon sources (CO2, glucose, and amino acids) synchronously to grow and accumulate DHA. Cell growth, the uptake of glucose and amino acids, and DHA production were significantly affected by CO2 enrichment. The maximum biomass concentration of 3.85 g L−1 was achieved with 3 % CO2. And the maximum DHA yield was 65.5 mg L−1 d−1. To enhance DHA production, a two-stage cultivation strategy was successfully developed by this work. The maximum DHA yield of the two-stage culture was elevated by 2.3-fold. It is feasible to produce DHA by Isochrysis galbana using leftover dough under CO2 enrichment.

Optimal Feeding Strategy in Fermentation of Docosahexaenoic Acid Production by Schizochytrium sp.

AbstractFed‐batch fermentation has the potential to increase the production of docosahexaenoic acid (DHA) in Schizochytrium sp. which can provide additional nutrients. The feeding strategy in fed‐batch fermentation is one of the important aspects that could help in improving the DHA yield. An enhanced scatter search (eSS) method and the control vector parametrization (CVP) approach were applied to generate the optimal feeding trajectory numerically. Three objective functions were considered, namely, maximizing the DHA concentration, minimizing the final time, and maximizing the economic function. The shortest time and maximum DHA could be determined simultaneously from the optimal feeding trajectory in maximizing the economic function.

Metabolic Engineering to Improve Docosahexaenoic Acid Production in Marine Protist Aurantiochytrium sp. by Disrupting 2,4-Dienoyl-CoA Reductase

Docosahexaenoic acid (DHA) has attracted attention from researchers because of its pharmacological and nutritional importance. Currently, DHA production costs are high due to fermentation inefficiency; however, improving DHA yield by metabolic engineering in thraustochytrids is one approach to reduce these costs. In this study, a high-yielding (53.97% of total fatty acids) DHA production strain was constructed by disrupting polyunsaturated fatty acid beta-oxidation via knockout of the 2,4-dienyl-CoA reductase (DECR) gene (KO strain) in Aurantiochytrium sp. Slight differences in cell growth was observed in the wild-type and transformants (OE and KO), with cell concentrations in stationary of 2.65×106, 2.36×106 and 2.56×106 cells mL-1 respectively. Impressively, the KO strain yielded 21.62% more neutral lipids and 57.34% greater DHA production; moreover, the opposite was observed when overexpressing DECR (OE strain), with significant decreases of 30.49% and 64.61%, respectively. Furthermore, the KO strain showed a prolonged DHA production period with a sustainable increase from 63 to 90 h (170.03 to 203.27 mg g−1 DCW), while that of the wildtype strain decreased significantly from 150.58 to 140.10 mg g−1 DCW. This new approach provides an advanced proxy for the construction of sustainable DHA production strains for industrial purposes and deepens our understanding of the metabolic pathways of Aurantiochytrium sp.