DHA Production Research Articles

A new synthetic medium for the optimization of docosahexaenoic acid production in Crypthecodinium cohnii.

The heterotrophic microalgae Crypthecodinium cohnii was usually cultivated in complex medium containing glucose, yeast extract and sea salt. For the preparation of DHA with highest purity, a new defined medium without the yeast extract was developed. Different inoculated densities, C/N ratios, temperatures, culture volumes and glucose additions were investigated to optimize the algal growth rate and DHA production. The growth period in C. cohnii was shortened from 12-14 days to 7-8 days, the OD600 was enhanced from 2.0 to 3.0, the glucose consumption was accelerated and used up on day 3-4, and the DHA content in culture were increased from 10 to 45 nmoles/300 μl batch. It was found that C. cohnii had optimal growth and DHA accumulation in 25 °C, 0.2 inoculated density, 5-10 C/N ratio, 5:1 air/culture volume ratio. This is the first time DHA production using C.cohnii has been optimized in synthetic medium. This allows preparation of uniformly radiolabeled 13C- and 14C-DHA.

Effect of airflow conditions on growth and simultaneously DHA and squalene production by Aurantiochytrium sp. PRA-276

Effect of airflow conditions on growth and simultaneously DHA and squalene production by Aurantiochytrium sp. PRA-276

Subtle Control of Carbon Chain Length in Polyunsaturated Fatty Acid Synthases.

Some marine bacteria synthesize docosahexaenoic acid (DHA; C22) and eicosapentaenoic acid (EPA; C20) by enzyme complexes composed of four subunits (A-D). We recently revealed that β-ketoacyl synthase (KSC)/chain length factor (CLF)-like domains in the "C" subunit of DHA synthase catalyzed the last elongation step (C20 to C22) even though their amino acid sequences are very similar to those of EPA synthase. To investigate the amino acid residues controlling the product chain length, conserved residues in the KSC/CLF-like domains in DHA synthase were replaced with corresponding EPA synthase residues. Among 12 mutants, two CLF-like domain-mutated genes completely lost DHA productivity and produced trace amounts of EPA when coexpressed with dha-ABD in Escherichia coli, whereas when coexpressed with epa-ABD, they produced the same amounts of EPA as epa-ABCD. These results suggest that the product profiles were subtly controlled by several amino acid residues.

Fed-batch fermentation of mixed carbon source significantly enhances the production of docosahexaenoic acid in Thraustochytriidae sp. PKU#Mn16 by differentially regulating fatty acids biosynthetic pathways.

This study reports comparative evaluation of the growth and DHA productivity of the thraustochytrid strain Thraustochytriidae PKU#Mn16 fermented with seven different substrate feeding strategies. Of these strategies, fed-batch fermentation of the mixed substrate (glucose & glycerol) yielded the maximum growth (52.2 ± 1.5 g/L), DHA yield (Yp/s: 8.65) and productivity (100.7 ± 2.9 mg/L-h), comparable with those of previously reported Aurantiochytrium strains. Transcriptomics analyses revealed that glucose upregulated some genes of the fatty acid synthase pathway whereas glycerol upregulated a few genes of the polyketide synthase pathway. Co-fermentation of the mixed substrate differentially regulated genes of these two pathways and significantly enhanced the DHA productivity. Furthermore, some genes involved in DNA replication, phagosome, carbon metabolism, and β-oxidation were also found to alter significantly during the mixed-substrate fermentation. Overall, this study provides a unique strategy for enhancing growth and DHA productivity of the strain PKU#Mn16 and the first insight into the mechanisms underlying mixed-substrate fermentation.

Transcriptome Mechanism of Utilizing Corn Steep Liquor as the Sole Nitrogen Resource for Lipid and DHA Biosynthesis in Marine Oleaginous Protist Aurantiochytrium sp.

In the current study, corn steep liquor (CSL) is evaluated as an ideal raw agro-material for efficient lipid and docosahexaenoic acid DHA production by Aurantiochytrium sp. Low CSL level in medium (nitrogen deficiency) stimulated the biosynthesis of lipids and DHA while inhibiting cellular growth. The transcriptomic profiles of the Aurantiochytrium sp. cells are analyzed and compared when cultured under high (H group), normal (N group), and low (L group) levels of CSL in the medium. The discriminated transcriptomic profiles from the three groups indicates that changes in CSL level in medium result in a global change in transcriptome of Aurantiochytrium sp. The overall de novo assembly of cDNA sequence data generated 61,163 unigenes, and 18,129 of them were annotated in at least one database. A total of 5105 differently expressed (DE) genes were found in the N group versus the H group, with 2218 downregulated and 2887 upregulated. A total of 3625 DE genes were found in the N group versus the L group, with 1904 downregulated and 1721 upregulated. The analysis and categorization of the DE genes indicates that the regulation mechanism of CSL involved in the perception and transduction of the limited nitrogen signal, the interactions between the transcription factors (TFs) and multiple downstream genes, and the variations in downstream genes and metabolites, in sequence, are illuminated for the first time in the current study.

Eutrophication reduces the nutritional value of phytoplankton in boreal lakes

Eutrophication (as an increase in total phosphorus [TP]) increases harmful algal blooms and reduces the proportion of high-quality phytoplankton in seston and the content of ω-3 long-chain polyunsaturated fatty acids (eicosapentaenoic acid [EPA] and docosahexaenoic acid [DHA]) in fish. However, it is not well-known how eutrophication affects the overall nutritional value of phytoplankton. Therefore, we studied the impact of eutrophication on the production (as concentration; μg L−1) and content (μg mg C−1) of amino acids, EPA, DHA, and sterols, i.e., the nutritional value of phytoplankton in 107 boreal lakes. The lakes were categorized in seven TP concentration categories ranging from ultra-oligotrophic (<5 μg L−1) to highly eutrophic (>50 μg L−1). Phytoplankton total biomass increased with TP as expected, but in contrast to previous studies, the contribution of high-quality phytoplankton did not decrease with TP. However, the high variation reflected instability in the phytoplankton community structure in eutrophic lakes. We found that the concentration of amino acids increased in the epilimnion whereas the concentration of sterols decreased with increasing TP. In terms of phytoplankton nutritional value, amino acids, EPA, DHA, and sterols showed a significant quadratic relationship with the lake trophic status. More specifically, the amino acid contents were the same in the oligo- and mesotrophic lakes, but substantially lower in the eutrophic lakes (TP > 35 μg L−1/1.13 μmol L−1). The highest EPA and DHA content in phytoplankton was found in the mesotrophic lakes, whereas the sterol content was highest in the oligotrophic lakes. Based on these results, the nutritional value of phytoplankton reduces with eutrophication, although the contribution of high-quality algae does not decrease. Therefore, the results emphasize that eutrophication, as excess TP, reduces the nutritional value of phytoplankton, which may have a significant impact on the nutritional value of zooplankton, fish, and other aquatic animals at higher food web levels.

Molecular and functional characterisation of a putative elovl4 gene and its expression in response to dietary fatty acid profile in Atlantic bluefin tuna (Thunnus thynnus).

Elongation of very long-chain fatty acid 4 (Elovl4) proteins are involved in the biosynthesis of very long-chain (>C24) fatty acids and in many teleost fish species they are key enzymes in the pathway for the production of docosahexaenoic acid (DHA; 22:6n-3) from eicosapentaenoic acid (EPA; 20:5n-3). Therefore, Elovl4 may be particularly important in Atlantic bluefin tuna (ABT; Thunnus thynnus) characterised by having high DHA to EPA ratios. The present study cloned and characterised both the function and expression of an elovl4 cDNA from ABT. The Elovl4 had an open reading frame of 915 base pairs encoding a putative protein of 304 amino acids. Alignment and phylogenetic analyses indicated that the Elovl4 isoform identified in the present study was an Elovl4b. Functional characterisation demonstrated that the Elovl4b enzyme had elongase activity towards all the polyunsaturated fatty acid (PUFA) substrates assayed. The ABT Elovl4b contributed to DHA biosynthesis by elongation of EPA and DPA to 24:5n-3, the latter being desaturated to 24:6n-3 by the action of fads2 (Δ6 desaturase). Additionally, the ABT Elovl4b has a role in the biosynthesis of very long-chain PUFA up to C34, compounds of key structural roles in neural tissues such as eye and brain, which had high levels of elovl4b transcripts. Surprisingly, while the relative expression of fads2, required for the production of DHA from EPA, was increased in liver of ABT fed a diet with reduced levels of EPA and DHA, expression of elovl4b was reduced. Results indicated that ABT has enzymes necessary for endogenous production of DHA from EPA and demonstrate that Elovl4b can effectively compensate for absence of Elovl2.

Optimization of culture condition for growth of the Aurantiochytrium sp. shy, isolated from Persian Gulf

In this study, a native microalgae strain with a high capability of DHA production has been isolated and purified from Mangrove shores in the Persian Gulf. Morphological and molecular identification based on 18S rRNA gene showed that the isolated strain belongs to Aurantiochytrium genus. In order to optimize the growth of this strain, various environmental factors were examined, including temperature(15, 20, 25, 30 and 35°C), salinity (10, 30 and 50 g/L) and different concentrations of nitrogen sources of Yeast extract, Peptone, Meat Extract and Monosodium glutamate, each of which being tested with 10 g/L concentrations. The findings show that the optimal growth conditions occur in 25-30°, pH 6 and presence of Meat Extract as a nitrogen source. In these conditions, the cellular biomass weight, fatty acids and DHA amounts were obtained as 7.34, 2.25 and 0.4 g/L, respectively. These results imply that the new isolated strain of Aurantiochytrium sp.shy is suitable for lipid production.

Characterization of a hyperthermophilic phosphatase from Archaeoglobus fulgidus and its application in in vitro synthetic enzymatic biosystem

BackgroundHaloacid dehalogenase (HAD)-like hydrolases represent the largest superfamily of phosphatases, which release inorganic phosphate from phosphate containing compounds, such as sugar phosphates. The HAD-like phosphatases with highly substrate specificity, which perform irreversible dephosphorylation, are always integrated into in vitro synthetic enzymatic biosystems as the last enzymatic step for the cost-efficient production of biochemicals. Therefore, identification and characterization of substrate specificity of HAD-like phosphatases are important for exploring their application.ResultsIn this study, a hyperthermophilic HAD-like phosphatase from Archaeoglobus fulgidus (AfPase) was cloned, expressed, and characterized. AfPase was identified as a type I Mg2+-dependent HAD-like phosphatase with high optimal temperature and thermostability. Among the tested phosphate containing compounds, AfPase exhibited the highest catalytic activity on p-nitrophenyl phosphate, followed by dihydroxyacetone phosphate (DHAP). On the basis of the high catalytic activity of AfPase to generate 1,3-dihydroxyacetone (DHA) from DHAP, an in vitro synthetic enzymatic biosystem containing this phosphatase and other five enzymes was constructed for the biosynthesis of DHA from inexpensive maltodextrin in one pot. About 14 mM (1.26 g/L) DHA was produced from 10 g/L maltodextrin.ConclusionsA hyperthermophilic HAD-like phosphatase from Archaeoglobus fulgidus was characterized carefully, and the success of an in vitro synthetic enzymatic biosystem containing this phosphatase provided a promising approach for DHA production from maltodextrin.

Research of 1,3-Dihydroxyacetone Production by Overexpressing Glycerol Transporter and Glycerol Dehydrogenase

1,3-Dihydroxyacetone (DHA), a natural ketose, is widely used in the chemical, cosmetic, and pharmaceutical industries. The current method for DHA production is Gluconobacter oxydans (G. oxydans) fermentation, but the high concentration of glycerol in the fermentation broth inhibits cells growth. To overcome this obstacle, in this study, we overexpressed the glycerol transporter (GlpFp) by the use of promoters PtufB, Pgmr, Pglp1, and Pglp2 in G. oxydans 621H. The results show that the glycerol tolerances of strains overexpressing GlpF were all much better than that of the control strain. The glycerol dehydrogenase gene (Gdh) was overexpressed by the promoters PtufB and Pgdh, which increased the DHA titer by 12.7% compared with that of the control group. When GlpF and Gdh genes were co-overexpressed in G. oxydans 621H, the OD600 value of the engineered strains all increased, but the DHA titers decreased in different degrees, as compared with strains that overexpressed only Gdh. This study provides a reference for future research on DHA production.

Boosting productivity of heterotrophic microalgae by efficient control of the oxygen transfer coefficient using a microbubble sparger

We isolated and characterized an oleaginous Thraustochytrid microalga. Based on 18 s rRNA sequencing, we classified this strain as Schizochytrium sp. SH103. Growth of these cells in a 5 L fermentor with a microbubble-type sparger (MTS) efficiently increased the oxygen transfer coefficient (OTC), while inducing only low external stress. For fermentation under conditions of low agitation (100 rpm) and aeration (3 L/min), the OTC was 8.6-fold higher using a MTS than a general type sparger (GTS). Under these same conditions, dry cell weight (DCW) productivity (0.54 vs. 1.26 g/L·h) and total lipid productivity (0.29 vs. 0.61 g/L·h) were each about 2.2-fold higher using a MTS than a GTS. Under conditions that optimized the OTC in a MTS fermentor (876 h−1), DCW productivity, total lipid productivity and DHA productivity were each 1.3-fold greater than non-optimized condition. Fed-batch fermentation experiments indicated the maximal DCW was 100.6 g/L at 48 h, maximal DCW productivity was 2.1 g/L·h, maximal lipid content was 48.6 g/L at 48 h, and lipid productivity was 1.0 g/L·h. Additionally, the results of experiments using a 50 L MTS fermentor (96.0 g/L DCW and 44.3 g/L total lipids at 48 h) were similar to those using the 5 L fermentor. Our results suggest that use of a MTS may help to achieve the efficient fermentation of heterotrophic microalgae for high cell densities.

Genetic modification of the thraustochytrid Aurantiochytrium sp. 18W-13a for cellobiose utilization by secretory expression of β-glucosidase from Aspergillus aculeatus

Thraustochytrids are osmoheterotrophic protists that are emerging as a promising group of oleaginous microorganisms due to their high DHA, EPA and palmitic acid production. Squalene, a triterpene hydrocarbon known for its antioxidant, antitumorigenic and emollient properties, is accumulated in some strains of thraustochytrids especially in the genus Aurantiochytrium. Thraustochytrids can produce extracellular enzymes to degrade organic matter as their means of nutrition. Many studies attempt to grow thraustochytrids in cost-effective substrates such as lignocellulosic biomass. As the first step towards cellulose utilization, we genetically modified Aurantiochytrium sp. strain 18W-13a to express and secrete a highly active cellulase, β-glucosidase from Aspergillus aculeatus (AaBgl). The transformant strain, AaBgl+, exhibited increasing growth and enzyme activity under cellobiose as the sole carbon source. Native PAGE zymogram showed an active β-glucosidase enzyme in the supernatant of the AaBgl+ strain. Both wild-type and AaBgl+ strains can produce squalene and fatty acids DHA and DPA. This work is one of the first reports in targeted secretion of a functional enzyme in thraustochytrids. Moreover, enhanced expression of cellulases has never been done in thraustochytrids. We hope that this study could pave way for establishing consolidated bioprocessing thraustochytrid strains.

Transcriptomic Mechanism of the Phytohormone 6-Benzylaminopurine (6-BAP) Stimulating Lipid and DHA Synthesis in Aurantiochytrium sp.

The phytohormone 6-benzylaminopurine (6-BAP) significantly improves lipid synthesis of oleaginous microorganisms with the great potential applied in lipid production. In the current study, the lipid and DHA productions in oleaginous Aurantiochytrium sp. were found to be improved by 48.7% and 55.3%, respectively, induced by 6-BAP treatments. Then, using high-throughput RNA-seq technology, the overall de novo assembly of the cDNA sequence data generated 53871 unigenes, and 15902 of these were annotated in at least one database. The comparative transcriptomic profiles of cells with and without 6-BAP treatments revealed that a total of 717 were differently expressed genes (DE), with 472 upregulated and 245 downregulated. Further annotation and categorization indicated that some DE genes were involved in pathways crucial to lipid and DHA productions, such as fatty acid synthesis, central carbon metabolism, transcriptional factor, signal transduction, and mevalonate pathway. A regulation mode of 6-BAP, in turn, perception and transduction of 6-BAP signal, transcription factor, expression regulations of the downstream genes, and metabolic changes, respectively, was put forward for the first time in the present study. This research illuminates the transcriptomic mechanism of phytohormone stimulation of lipid and DHA production in an oleaginous microorganism and provides the potential targets modified using genetic engineering for improving lipid and DHA productivity.

Fatty Acid Profiles and Production in Marine Phytoplankton.

Microalgae are the primary producers of carbon in marine ecosystems, fixing carbon and subsequently generating various biomolecules such as carbohydrates, proteins and lipids. Most importantly, microalgae are the generators and main suppliers of ω3 polyunsaturated fatty acids (ω3PUFA) in the marine ecosystem, which have a fundamental importance for the functioning and quality of the whole marine food web. A meta-analysis of over 160 fatty acid profiles of 7 marine phytoplankton phyla reveals not only a phyla-specific, but also a highly class-specific PUFA production of marine phytoplankton. The highest EPA (Eicosapentaenoic acid; 20:5ω3) production per total fatty acids was found in 2 classes of Haptophyta and in Ochrophyta, while Dinophyta and the Haptophyte Emiliana huxleyi show the highest production of DHA (Docosahexaenoic acid; 22:6ω3). An important precursor for EPA, Stearidonic acid (SDA, 18:4ω3) is found in high proportions in Cryptophyta and the Chlorophta class Pyramimonadophyceae. Per unit of carbon, Chlorophyta and Cyanobacteria were the poorest producers of highly unsaturated fatty acids (HUFA). The remaining phyla had a similar HUFA contribution per unit of carbon but with different compositions. The nutritional and environmental effects on the phytoplankton PUFA production is summarized and shows a lowering of the PUFA content under stressful environmental conditions.

N-3 PUFA biosynthesis by the copepod Apocyclops royi documented using fatty acid profile analysis and gene expression analysis.

ABSTRACTThe cyclopoid copepod Apocyclops royi (Lindberg 1940) is one of two dominant mesozooplankton species in brackish Taiwanese aquaculture ponds. Periodically low n-3 polyunsaturated fatty acid (PUFA) content in seston could potentially be a limiting factor for zooplankton diversity. Apocyclops royi’s potential ability to biosynthesize n-3 PUFA was investigated through a short-term feeding experiment on four species of microalgae. Furthermore, we analyzed the expression of genes encoding putative fatty acid elongase (ELO) and desaturase (FAD) enzymes in A. royi on long-term diets of the PUFA-poor Dunaliella tertiolecta and the PUFA-rich Isochrysis galbana. The copepods exhibited high contents of docosahexaenoic acid (DHA, C22:6n-3) (>20% of total fatty acid) even when DHA-starved for two generations, and no significant differences were found in absolute DHA content between treatments. Transcripts correlating to the four enzymes Elovl4, Elovl5, Fad Δ5 and Fad Δ6 in the n-3 PUFA biosynthetic pathway were identified. Gene expression analysis revealed a significantly higher expression of two desaturases similar to Fad Δ6 in copepods fed PUFA-lacking algae compared to copepods fed algae with high PUFA content. These findings suggest a highly active n-3 PUFA biosynthesis and capability of DHA production in A. royi when fed low-PUFA diets.

A Novel Dietary Source of EPA and DHA: Metabolic Engineering of an Important Freshwater Species—Common Carp by fat1-Transgenesis

Omega-3 polyunsaturated fatty acids (n-3 PUFAs), such as eicosapentaenoic acid (20:5n-3, EPA) and docosahexaenoic acid (22:6n-3, DHA), are essential for neural development and human health. The n-3 PUFAs are mainly obtained from marine fish by dietary intake. Freshwater fish species usually contain low level of n-3 PUFAs due to the lack of n-3 PUFAs in their food chain. In this study, we report on the substantial production of EPA and DHA in a globally important freshwater fish species, common carp (Cyprinus carpio). This was achieved by introducing an "all-fish" transgene CA:fat1 containing the fish codon-optimized omega-3 desaturase gene (fat1) driven by the common carp β-actin promoter (CA). Through a sperm sample screening method, we successfully generated fat1-positive F1 transgenic population with high efficiency. In F1 population, the muscle contents of ALA (18:3n-3), EPA and DHA were significantly increased when compared with non-transgenic siblings. Thereafter, four independent F2 heterozygous lines were obtained from 4 F1 transgenic males and a detailed comparison of fatty acids profile and growth performance was carried out for these 4 lines. All fat1-transgenic common carps from 4 lines showed an evident decrease in n-6 PUFA contents and a substantial increase in n-3 PUFA contents, among which line 4 stands out, showing a statistically significant increase in all 4 types of n-3 PUFAs including ALA (4.4-fold increase, p < 0.001), EPA (4.8-fold increase, p < 0.01), C22:5n-3 (DPA, 2.4-fold increase, p < 0.05), and DHA (1.9-fold increase, p < 0.05). Therefore, the line 4 was selected as the optimized breeding stock for further study, and the proximate nutrition composition and PUFA synthesis pathway were analyzed. Our study demonstrates that in the transgenic group, the muscular lipid content did not change, while fat accumulations in the internal organs and especially in the liver were significantly decreased as a result of hyperactivation of fatty acid oxidation process. Finally, we conclude that the "all-fish" CA:fat1-transgenic freshwater fish-common carp-can serve as a novel healthy dietary source of n3-PUFAs, especially EPA and DHA.

Different DHA or EPA production responses to nutrient stress in the marine microalga Tisochrysis lutea and the freshwater microalga Monodus subterraneus

This study investigated the effect of nitrogen (N) and phosphorous (P) stress on the production of DHA or EPA and total fatty acids (TFAs) in the marine microalga Tisochrysis lutea and the freshwater microalga Monodus subterraneus. Five N or P starvation/limitation conditions (N sufficient and P limited, N sufficient and P starved, N starved and P sufficient, N starved and P limited, and N and P starved) and one N and P sufficient condition (control) were studied. The results demonstrated that the proportion of DHA or EPA among TFAs and production in the microalgae suspensions decreased (57%, 73% for N stress and 18%, 51% for P stress, respectively) under N or P stress in both microalgae compared with the N and P sufficient group. Differently, DHA dry weight content of T. lutea decreased significantly, and EPA dry weight content of M. subterraneus decreased slightly under N starved conditions. Clear differences in TFA content/production and the relationship between TFA and DHA or EPA production/content and CO2 fixation were observed between the two microalgae. These results give a new sight on the difference between marine microalgae and freshwater microalgae. Meanwhile, it gave a potential application to produce DHA or EPA and TFA combining with CO2 fixation by these microalgae.

Highly selective oxidation of glycerol over Bi/Bi3.64Mo0.36O6.55 heterostructure: Dual reaction pathways induced by photogenerated 1O2 and holes

Selective oxidation of glycerol to produce aimed high-value added products is of great importance in chemical industry. Photocatalytic oxidation provides a promising and green strategy for selective glycerol oxidation. In this work, we develop a Bi/Bi3.64Mo0.36O6.55 heterostructure via a facile solvothermal method for the selective oxidation glycerol to 1, 3-dihydroxyacetone (DHA) in water under visible light irradiation. The excellent performance in activity and selectivity of Bi/Bi3.64Mo0.36O6.55 heterostructure for DHA production is attributed to a dual-pathway photocatalytic reaction process. The mass production 1O2 ascribed to the reduced energy gap (ΔEST), the enhanced spin-orbit coupling (SOC) and the presence of oxygen vacancy is beneficial for the selective oxidation of glycerol to DHA. Simultaneously, the metallic bismuth in the heterostructure promotes the separation of photogenerated holes with efficient redox potential and facilitates the binding bismuth with ortho-hydroxyl in glycerol, thus enhancing the yield and selectivity of DHA production. This work provides a novel strategy and thorough understanding of the development of highly efficient bismuth-based photocatalyst for selective oxidation in organic reactions.

Rewiring metabolic network by chemical modulator based laboratory evolution doubles lipid production in Crypthecodinium cohnii

Dietary omega-3 long-chain polyunsaturated fatty acids docosahexaenoic acid (DHA, C22:6) can be synthesized in microalgae Crypthecodinium cohnii; however, its productivity is still low. Here, we established a new protocol termed as “chemical modulator based adaptive laboratory evolution” (CM-ALE) to enhance lipid and DHA productivity in C. cohnii. First, ACCase inhibitor sethoxydim based CM-ALE was applied to redirect carbon equivalents from starch to lipid. Second, CM-ALE using growth modulator sesamol as selection pressure was conducted to relive negative effects of sesamol on lipid biosynthesis in C. cohnii, which allows enhancement of biomass productivity by 30% without decreasing lipid content when sesamol was added. After two-step CM-ALE, the lipid and DHA productivity in C. cohnii was respectively doubled to a level of 0.046 g/L/h and 0.025 g/L/h in culture with addition of 1 mM sesamol, demonstrating that this two-step CM-ALE could be a valuable approach to maximize the properties of microalgae.

Different fermentation strategies by Schizochytrium mangrovei strain pq6 to produce feedstock for exploitation of squalene and omega-3 fatty acids.

Schizochytrium mangrovei strain PQ6 was investigated for coproduction of docosahexaenoic acid (C22: 6ω-3, DHA) and squalene using a 30-L bioreactor with a working volume of 15L under various batch and fed-batch fermentation process regimes. The fed-batch process was a more efficient cultivation strategy for achieving higher biomass production rich in DHA and squalene. The final biomass, total lipid, unsaponifiable lipid content, and DHA productivity were 105.25g·L-1 , 43.40% of dry cell weight, 8.58% total lipid, and 61.66mg·g-1 ·L-1 , respectively, after a 96h fed-batch fermentation. The squalene content was highest at 48h after feeding glucose (98.07mg·g-1 of lipid). Differences in lipid accumulation during fermentation were correlated with changes in ultrastructure using transmission electron microscopy and Nile Red staining of cells. The results may be of relevance to industrial-scale coproduction of DHA and squalene in heterotrophic marine microalgae such as Schizochytrium.