Marine Microalga Schizochytrium Research Articles

Marine microalgae Schizochytrium demonstrates strong production of essential fatty acids in various cultivation conditions, advancing dietary self-sufficiency

IntroductionPolyunsaturated fatty acids (PUFAs) are essential nutrients that humans obtain from their diet, primarily through fish oil consumption. However, fish oil production is no longer sustainable. An alternative approach is to produce PUFAs through marine microalgae. Despite the potential of algae strains to accumulate high concentrations of PUFAs, including essential fatty acids (EFAs), many aspects of PUFA production by microalgae remain unexplored and their current production outputs are frequently suboptimal.MethodsIn this study, we optimized biomass and selected ω-3 PUFAs production in two strains of algae, Schizochytrium marinum AN-4 and Schizochytrium limacinum CO3H. We examined a broad range of cultivation conditions, including pH, temperature, stirring intensity, nutrient concentrations, and their combinations.ResultsWe found that both strains grew well at low pH levels (4.5), which could reduce bacterial contamination and facilitate the use of industrial waste products as substrate supplements. Intensive stirring was necessary for rapid biomass accumulation but caused cell disruption during lipid accumulation. Docosahexaenoic acid (DHA) yield was independent of cultivation temperature within a range of 28–34°C. We also achieved high cell densities (up to 9 g/L) and stable DHA production (average around 0.1 g/L/d) under diverse conditions and nutrient concentrations, with minimal nutrients required for stable production including standard sea salt, glucose or glycerol, and yeast extract.DiscussionOur findings demonstrate the potential of Schizochytrium strains to boost industrial-scale PUFA production and make it more economically viable. Additionally, these results may pave the way for smaller-scale production of essential fatty acids in a domestic setting. The development of a new minimal culturing medium with reduced ionic strength and antibacterial pH could further enhance the feasibility of this approach.

Integrated Process for Schizochytrium Oil Extraction, Enzymatic Modification of Lipids and Concentration of DHA Fatty Acid Esters Using Alternative Methodologies.

Marine microalgae Schizochytrium sp. have a high content of docosahexaenoic acid (DHA), an omega-3 fatty acid that is attracting interest since it prevents certain neurodegenerative diseases. The obtention of a bioactive and purified DHA fatty acid ester using a whole-integrated process in which renewable sources and alternative methodologies are employed is the aim of this study. For this reason, lyophilized Schizochytrium biomass was used as an alternative to fish oil, and advanced extraction techniques as well as enzymatic modification were studied. Microalgal oil extraction was optimized via a surface-response method using pressurized liquid extraction (PLE) obtaining high oil yields (29.06 ± 0.12%) with a high concentration of DHA (51.15 ± 0.72%). Then, the enzymatic modification of Schizochytrium oil was developed by ethanolysis using immobilized Candida antarctica B lipase (Novozym® 435) at two reaction temperatures and different enzymatic loads. The best condition (40 °C and 200 mg of lipase) produced the highest yield of fatty acid ethyl ester (FAEE) (100%) after 8 h of a reaction attaining a cost-effective and alternative process. Finally, an enriched and purified fraction containing DHA-FAEE was obtained using open-column chromatography with a remarkably high concentration of 93.2 ± 1.3% DHA. The purified and bioactive molecules obtained in this study can be used as nutraceutical and active pharmaceutical intermediates of marine origin.

Trypanosoma cruzi Tc24 Antigen Expressed and Orally Delivered by Schizochytrium sp. Microalga is Immunogenic in Mice.

Chagas disease-caused by the parasite Trypanosoma cruzi-is a neglected tropical disease for which available drugs are not fully effective in the chronic stage and a vaccine is not available yet. Microalgae represent a promising platform for the production and oral delivery of low-cost vaccines. Herein, we report a vaccine prototype against T. cruzi produced in a microalgae platform, based on the candidate antigen Tc24 with a C terminus fusion with the Co1 peptide (Tc24:Co1 vaccine prototype). After modeling the tertiary structure, in silico studies suggested that the chimeric protein is antigenic, not allergenic, and molecular docking indicated binding with Toll-like receptors 2 and 4. Thus, Tc24:Co1 was expressed in the marine microalga Schizochytrium sp., and Western blot confirmed the expression at 48h after induction, with a yield of 632µg/L of algal culture (300μg/g of lyophilized algal cells) as measured by the enzyme-linked immunosorbent assay (ELISA). Upon oral administration of whole-cell Schizochytrium sp. expressing Tc24:Co1 (7.5µg or 15µg of Tc24:Co1 doses) in mice, specific serum IgG and intestinal mucosa IgA responses were detected in addition to an increase in serum Th1/Th2 cytokines. In conclusion, Schizochytrium sp.-expressing Tc24:Co1 is a promising oral vaccine prototype to be evaluated in an animal model of Trypanosoma cruzi infection.

Comparative life cycle assessment of heterotrophic microalgae Schizochytrium and fish oil in sustainable aquaculture feeds

Fish oil is primarily extracted from small marine pelagic fishes, reducing their availability for marine wildlife forage and artisanal fishing catches that support food security in lower income coastal nations. A primary use of fish oil is in feeds for aquaculture, the world’s fastest growing food sector. Efforts to transition fed aquaculture to sustainability includes replacing fish oil in aquafeeds with more environmentally responsible alternative ingredients. The heterotrophic marine microalga Schizochytrium sp., one of the first commercialized alternatives, lacks an open-access, systematic analysis of environmental impacts of substituting fish oil with heterotrophic microalgae from biorefineries. This study compared the “cradle to factory-gate” life cycle impacts of fish oil to whole-cell or extracted oil of Schizochytrium combined with canola oil. We conducted an attributional life cycle assessment using inventory data collected from published literature and patents and received feedback on commercial relevance of model assumptions from industry advisors. We examined sugar from a Brazilian sugarcane biorefinery and sucrose from U.S. sugar beets as feedstocks for heterotrophic cultivation of Schizochytrium; and compared life cycle impacts of extracting Schizochytrium oil using solvent-free microwave extraction to conventional solvent extraction. Results were that: cultivation processes had the largest overall effect for both products in both regions; whole-cell Schizochytrium combined with canola oil had significantly lower environmental impacts, in all assessed categories, than Schizochytrium oil blended with canola oil; and conventional solvent extraction had significantly lower environmental impacts compared to solvent-free microwave extraction except global warming potential. Schizochytrium products, compared to fish oil, had substantially lower biotic resource depletion and, in the case of whole cells combined with canola oil, had significantly lower global warming potential but higher impacts for all other categories, primarily because commercial Schizochytrium production used sugar feedstocks as carbon and energy sources. The mix of lower and higher environmental impacts of Schizochytrium products illustrates the importance of openly identifying environmental trade-offs to inform evidence-based decisions for commercial practices. Environmental impacts should also be weighed against potential human health benefits of maintaining omega-3 fatty acids and avoiding contaminants in fish flesh when considering alternatives to fish oil.

Zinc Finger Protein LipR Represses Docosahexaenoic Acid and Lipid Biosynthesis in Schizochytrium sp.

The heterotrophic marine microalgae Schizochytrium sp. is an important industrial producer of docosahexaenoic acid (DHA). Increased production of DHA and lipids in Schizochytrium sp. has been achieved by standard fermentation optimization and metabolic engineering methods; however, regulatory mechanisms for DHA and lipid biosynthesis remain unknown. In this study, the C2H2 zinc finger protein LipR was identified in Schizochytrium sp. ATCC 20888 by transcriptional analysis. Deletion of the lipR gene significantly (P < 0.001) increased production of total lipids and DHA by 33% and 48%, respectively. LipR repressed DHA and lipid production by directly inhibiting transcription of polyunsaturated fatty acid (PUFA) and fatty acid synthase (FAS) genes (pfa1, pfa2, pfa3, and fas). Specific binding of LipR to 9-bp recognition sequence 5'-(C/A)(A/G)CCATCTT-3' in upstream regions of target genes was demonstrated by electrophoretic mobility shift assays (EMSAs) and DNase I footprinting assays. Expression of several key genes (acc, acl, ampD, fabD, mae, zwf, and dga1) related to levels of precursors and NADPH, and to triacylglycerol storage rate, were also directly repressed by LipR. Our findings, taken together, indicate that the evolutionarily unique regulator LipR is an essential repressor of DHA and saturated fatty acid biosynthesis in Schizochytrium sp. IMPORTANCE Regulatory mechanisms for DHA and saturated fatty acid biosynthesis in the heterotrophic marine microalgae Schizochytrium sp. are unclear. We demonstrate here that deletion of the gene (lipR) encoding the C2H2 zinc finger protein LipR promotes DHA and saturated fatty acid production in this genus. LipR acts as a key repressor of such production by binding to 9-bp consensus sequence 5'-(C/A)(A/G)CCATCTT-3' in the upstream regions of polyunsaturated fatty acid and fatty acid synthase genes (pfa1, pfa2, pfa3, and fas), and genes related to levels of precursors and NADPH (acc, acl, ampD, fabD, mae, and zwf), and to triacylglycerol storage rate (dga1). This is the first demonstration that a regulator inhibits synthesis of DHA and lipids in Schizochytrium sp. by directly controlling transcription of PUFA synthase and fas genes. Manipulation of the lipR gene provides a potential strategy for enhancing accumulation of polyunsaturated fatty acids and lipids in thraustochytrids.

Effects of co-culturing Schizochytrium sp. and Escherichia coli cells on biomass and Docosahexaenoic acid (DHA) production

Heterotrophic marine microalga Schizochytrium sp. is one of the most studied microorganisms for docosahexaenoic acid (DHA) production. Severeal strategies were reported to enhance DHA production, including co-culturing algal cells with different microorganisms. In this study, Schizochytrium sp. and Escherichia coli were co-cultured to examine the effect of bacterial cells on the algal growth and DHA production. The cells were incubated for 168 h and recovered to analyze biomass production, lipid content and DHA yield in the mixed culture medium. Cultivation of algal and bacterial species together decreased the biomass production (g/L), total lipid concentration (ml/L), DHA yield (g/L) and DHA percentage in lipid content about 4.1, 1.7, 3.8 and 2.2 folds, respectively, compared to algal monoculture. The only increasing amount was obtained with DHA yield per biomass (mg/gCDW) which was about 1.1 fold higher in the mixed culture. The results showed that presence of Escherichia coli cells in the medium affected the growth of Schizochytrium sp. cells and DHA production negatively. It was estimated that the interaction between algal and bacterial cells were competition instead of mutualistic interaction in which bacterial cells outcompeted the algal cells and limited the cell density increase of algal cells in the mixed culture.

Cultivation and extraction of omega 3-6 fatty acids from the heterotrophic marine microalga Schizochytrium mangrovei TB17 to make a functional food

The objective of this study was to investigate the different fermentation conditions for Schizochytrium mangrovei TB17 biomass production rich in omega-3 and omega-6 fatty acids to determine the optimal conditions for bio-oil extraction from the algal biomass and to study the pharmacological effects of this bio-oil in experimental animal models. After 108 h of fed-batch fermentation, the cell density, dry biomass, lipid contents and docosahexaenoic acid (DHA) contents reached 392.53±3.89×106 cells/mL, 100.41±3.17 g/L, 41.04±0.87% dry cell weight (DCW) and 33.33±1.96% total fatty acids (TFAs) respectively. The in situ transesterification producing bio-oil rich in omega 3-6 fatty acids from the biomass of the TB17 strain reached a yield of TFAs of 45.02±1.37% DCW. The yields of PUFAs and SFAs were 30.02±0.38% and 69.98±0.53% of TFA respectively. The bio-oil mainly contains DHA and EPA accounting for 74.04±0.25% and 10.97±0.43% of the TFAs respectively. The bio-oil met the Vietnam food safety standard. According to the results of the acute in mice and the subchronic oral toxicity in rats for 90 days, the bio-oil rich in omega 3-6 fatty acids is safe and has the ability to improve memory and learning ability in mice which can be made functional food oil capsules for human.

Changes in the Rumen Bacteriome Structure and Enzymatic Activities of Goats in Response to Dietary Supplementation with Schizochytrium spp.

With the aim to produce functional dairy products enriched with polyunsaturated fatty acids (PUFA) by using feed supplements, radical changes could occur in the rumen microbiome. This work investigated the alterations of the rumen bacteriome of goats fed with PUFA-rich marine microalgae Schizochytrium spp. For the trial, twenty-four goats were divided into four homogenous clusters (six goats/treatment) according to their fat-corrected (4%) milk yield, body weight, and age; they were individually fed with alfalfa hay and a concentrate (F/C = 50/50). The concentrate of the control group (CON) contained no microalgae, while those of the treated groups were supplemented daily with 20 (ALG20), 40 (ALG40), and 60 g (ALG60) of Schizochytrium spp./goat. Rumen fluid samples were collected using a stomach tube during the 20th and 40th days of the experiment. The microbiome analysis using a 16S rRNA sequencing platform revealed that Firmicutes were decreased in microalgae-fed goats, while Bacteroidetes showed a tendency to increase in the ALG40 group due to the enhancement of Prevotellaceae. Cellulolytic bacteria, namely Treponema bryantii, Ruminococcus gauvreauii, R. albus, and R. flavefaciens, were decreased in the ALG40 group, resulting in an overall decrease of cellulase activity. In contrast, the amylolytic potential was significantly enhanced due to an upsurge in Ruminobacter amylophilus, Succinivibrio dextrinosolvens, and Fretibacterium fastidiosum populations. In conclusion, supplementing goats’ diets with 20 g Schizochytrium spp. could be considered a sustainable and efficient nutritional strategy to modulate rumen microbiome towards the development of dairy products enriched with bioactive compounds, while higher levels induced substantial shifts in determinant microbes’ populations.

Safety assessment and the effect of squalene isolated from schizochytrium mangrovei pq6 on serum hdl - cholesterol levels in animal models

In this paper, the acute and subchronic toxicity and the effect of squalene isolated from heterotrophic marine microalga Schizochytrium mangrovei PQ6 on the serum levels of HDL-C were investigated using animal models. The results of acute toxicity study showed that by oral administration of the squalene on albino mice at the highest dose of 58.25 g/kg of whole body of mice/day, the LD50 was not determined. Squalene at doses of 400 mg and 1,200 mg/kg/day for 60 consecutive days have allowed the normal behavior, body weight, hematological and biochemical parameters, liver and kidney functions, morphology of liver, kidney and spleen, total plasma cholesterol content, however, HDL-C level was higher in squalene treated mices compared to control group (p &lt; 0.05). In addition, at doses of 600 and 1,200 mg/kg/day for 60 continuous days, squalene treated mice showed the increase in HDL-C level and HDL-C/total cholesterol ratio and the decrease in the contents of LDL-C and VLDL-C without affecting the body and liver weights and levels of total cholesterol and triglyceride.

Safety Assessement And Pharmacological Effect of Algal Oil Omega 3-6 Capsule Rich In Dha, Dpa, Epa From Oil of Heterotrophic Marine Microalga &lt;i&gt; Schizochytrium mangrovei &lt;/i&gt; TB17 on the Experimental Animals

Recently, heterotrophic marine microalga Schizochytrium mangrovei has been shown to be rich in omega 3-6 fatty acids, mainly docosahexaenoic acid (DHA), ecosapentanoic acid (EPA) and docosapentanoic acid (DPA). These fatty acids play an important role on human health. In this article, we presented results of safety assessment and pharmacological effect of Algal Oil Omega 3-6 (AOO-3-6) which made from oil of S. mangrovei TB17 on the experimental animals after 90 days of use. The results of acute toxicity study showed that by oral administration of the AOO-3-6 on white mice at the highest dose of 15.27 g total of DHA, EPA, DPA / kg of whole body of mice/ day (the dosage was 113.63 times higher than the mice dose), the LD50 was not determined. It means that AOO-3-6 capsules was no signs toxicity. At doses of 78.4 mg and 352.8 mg of total of DHA, EPA, DPA/ kg of whole bode of rat/ day (effec-tive dose znd 4.5 times higher than the expected dose) for 90 continuous days on the mice didn’t affect the normal increment of body weight, hematological indices, biochemical indicators; function of liver and kid-ney; histopathology of liver, kidney, spleen of white rats. At the same time, at doses of 134.4 and 403.2 mg total of DHA, EPA and DPA/kg of body weight/day improved the ability to learn, remember on the mice. In addition, it also allowed building its reflexes sustainability in finding food to be faster with shorter reflectance time. As a result, AOO-3-6 capsules are safe and have the ability to improve memory, learning ability on the mouse which can be used for functional food for human health.

Marine microalgae bioengineered Schizochytrium sp. meal hydrolysates inhibits acute inflammation

Bioengineered marine microalgae Schizochytrium sp. is currently used to produce docosahexaenoic acid (DHA). However, following DHA extraction, the remaining protein-rich materials are not well utilized. In this study, we report that marine microalgae bioengineered Schizochytrium sp. hydrolysate (MESH), which exhibits a unique peptide profile as identified by Ultra Performance Liquid Chromatography coupled with Q-TOF mass spectrometry(UPLC/Q-TOF-MS), ameliorated bowel inflammation in mice. In a mouse model of experimentalcolitis induced by dextran sulfate sodium, compared with the control mice, the mice treated with MESH were highly resistant to colitis, as demonstrated by marked reductions in body weight loss, clinical colitis scores, colonic histological damage, and colonic inflammation. Mechanistically, MESH attenuated the induction of pro-inflammatory cytokines and increased the induction of anti-inflammatory cytokines. MESH also promoted the proliferation of colonic crypt stem cells and progenitor cells required for crypt repair. Collectively, these results reveal a previously unrecognized role of MESH as a potential anti-inflammatory treatment for colitis.

Extraction of bio - oil rich in omega 3-6 fatty acid using different methods from heterotrophic marine microalga Schizochytrium mangrovei

In recent years, producing bio-oil from microalgae has gained increasing interest. Schizochytrium mangrovei is a heterotrophic marine microalga that is capable of producing high levels of biomass and lipid. In this study, S. mangrovei strain TB17 was investigated for production of bio-oil consist of omega 3-6 fatty acids using different methods, including a one-stage (direction transesterification of biomass) or a two-stage method (crude oil extraction followed by transesterification). In the one-stage method, omega 3-6 fatty acid alkyl esters (FAAE) extracted from dried biomass reached to 96.36% of total fatty acids (TFA), and 12.71% of dry cell weight (DCW) in which content of docosahexaenoic acid (C22: 6ω-3, DHA), eicosapentaenoic acid (C20: 5ω-3, EPA) and docosapentaenoic acid (C22: 5ω-6, DPA) was accounted for 85.01% of TFA. However, using fresh biomass as feedstock was resulted in lower yield of FAAE (90.95% of TFA and 3.26% of DCW). In the two-stage method, when fresh and dried biomass were used as feedstock, omega 3-6 free fatty acids (FFA) were obtained with equivalent yield (99.07% and 99.83% of TFA; 17.09% and 14.85% of DCW, respectively) with DHA, EPA and DPA contents accounting for over 80% of TFA. Thus, fresh biomass could also be used to extract bio-oil instead of dried biomass. These results would contribute to reduce manufacturing cost of the bio-oil rich in omega 3-6 fatty acids from Schizochytrium in the future. Citation: Le Thi Thom, Nguyen Cam Ha, Dang Diem Hong, 2017. Extraction of bio - oil rich in omega 3-6 fatty acid using different methods from heterotrophic marine microalga Schizochytrium mangrovei. Tap chi Sinh hoc, 39(3): 359-366. DOI: 10.15625/0866-7160/v39n3.9829. *Corresponding author: ddhong60vn@yahoo.com Received 18 May 2017, accepted 20 August 2017

Using biomass of heterotrophic marine microalga Schizochytrium for improving docosahexaenoic acid (DHA, C22:6-3) in chicken eggs

The consumers’ demand for food products of superior health quality are growing. Many researches have been conducted to enhance nutritional value of foods as meat, eggs, and milk. Eggs are considered the most convenient way to supply bioactive nutrients. While protein and total lipid concentrations of eggs are not readity altered, fatty acid composition, mineral and vitamin contents can be modified by feeding the hens with certain dietary ingredients. In this study, we investigated the effect of adding microalga Schizochytrium mangrovei PQ6 biomass in basal diet on egg production and egg quality parameters, especially docosahexaenoic acid content (DHA, C22:6w-3) of laying hens. Total number of 60 line G3 laying hens (mix between line HA and Hungary, 51-60 weeks of age) were randomly allotted into one of three groups by 20 hens each (KPCS, KP1 and KP2). All groups of hens were fed basal diets of standard ingredients while feed of KP1 and KP2 group of hens was supplemented with S. mangrovei PQ6 biomass as a source of w-3 fatty acid in amount of 1 and 5 % respectively. The obtained results have shown that, after trial 10 weeks, addional microalgal biomass in the diet of hens did not effect on egg production and normal egg quality parameters (egg weight, ratio of yolk and albumen, Haugh unit, yolk color). However, adding 5% microalga biomass in diet improved markedly DHA content in egg (reached up to 234.19 mg/egg) compared to that in control (52.85 mg/egg) and 1% level of microalgal biomass in basal diet (54.15 mg/egg).

Towards Sustainable Aquafeeds: Complete Substitution of Fish Oil with Marine Microalga Schizochytrium sp. Improves Growth and Fatty Acid Deposition in Juvenile Nile Tilapia (Oreochromis niloticus).

We conducted a 84-day nutritional feeding experiment with dried whole cells of DHA-rich marine microalga Schizochytrium sp. (Sc) to determine the optimum level of fish-oil substitution (partial or complete) for maximum growth of Nile tilapia. When we fully replaced fish oil with Schizochytrium (Sc100 diet), we found significantly higher weight gain and protein efficiency ratio (PER), and lower (improved) feed conversion ratio (FCR) and feed intake compared to a control diet containing fish oil (Sc0); and no significant change in SGR and survival rate among all diets. The Sc100 diet had the highest contents of 22:6n3 DHA, led to the highest DHA content in fillets, and consequently led to the highest DHA:EPA ratios in tilapia fillets. Schizochytrium sp. is a high quality candidate for complete substitution of fish oil in juvenile Nile tilapia feeds, providing an innovative means to formulate and optimize the composition of tilapia juvenile feed while simultaneously raising feed efficiency of tilapia aquaculture and to further develop environmentally and socially sustainable aquafeeds. Results show that replacing fish oil with DHA-rich marine Sc improves the deposition of n3 LC PUFA levels in tilapia fillet. These results support further studies to lower Schizochytrium production costs and to combine different marine microalgae to replace fish oil and fishmeal into aquafeeds.

A novel feedstock for biodiesel production: The application of palmitic acid from Schizochytrium

With the growing energy crisis and environmental pollution worldwide, the environmental benefits of biodiesel have made it a more attractive product. However, the production of biodiesel feedstock can only satisfy a small fraction of the demand for transportation fuels, and the cost of this feedstock is the main obstacle to the commercialization of biodiesel. The marine microalgae Schizochytrium is a promising producer of biodiesel feedstock because of its short life cycle, high cell density, high lipid content and high palmitic acid (PA) content, all of which can improve the quality of biodiesel. In this study, a sequential optimization of the culture medium, based on response surface methodology (RSM), was employed to increase the PA production in Schizochytrium and lower the process cost. As a result, the PA production by Schizochytrium sp. S056 increased from 14.69 ± 0.62 g/L to 25.95 ± 0.11 g/L using the optimal conditions. In addition, the quality analysis of the crude lipid showed that the lipid produced by the microbial process is a promising feedstock for biodiesel production.

Overexpression of acetyl-CoA synthetase increased the biomass and fatty acid proportion in microalga Schizochytrium

High acetate accumulation was produced during glucose fermentation in high cell density cultures, which is harmful to cell growth. In order to reduce the negative impact of acetate accumulation on the fermentation products, we introduced the Escherichia coli acetyl-CoA synthetase (ACS) gene into the marine microalga Schizochytrium sp. TIO1101, generating genetically modified ACS transformants. The results of PCR and blotting analyses showed that the exogenous ACS gene was incorporated into the genome and successfully expressed. The engineered Schizochytrium increased the pH value and reduced the acetate concentration in the final fermentation medium significantly. Furthermore, the ACS transformants exhibited faster growth and glucose consumption rates than the wild-type strain. The biomass and fatty acid proportion of ACS transformants increased by 29.9 and 11.3 %, respectively. Taken together, the data suggest that ACS overexpression in Schizochytrium might improve the utilization of carbon resource and decrease the production of acetate byproduct. These results demonstrate that application of ACS in metabolic genetic engineering could improve the properties of Schizochytrium significantly.

Establishment of a transgene expression system for the marine microalga Schizochytrium by 18S rDNA-targeted homologous recombination

Schizochytrium is an established candidate for commercial production of long chain polyunsaturated fatty acids (PUFAs) that are important in human health and aquaculture. Genetic engineering technology has been applied successfully to increase the metabolites in many organisms. In order to use genetic engineering technology to enhance lipid accumulation in Schizochytrium for economically feasible PUFAs production, the transgene expression system should be established first. In the present study, we investigated a novel transgene expression system in Schizochytrium by 18S rDNA-targeted homologous recombination. The targeting vector pBS-18S-ZeoR contains a portion of 18S rDNA from Schizochytrium and the Zeocin resistance gene (Streptoalloteichus hindustanus bleomycin gene, Sh ble gene) expression cassette. This targeting vector was transformed into Schizochytrium by electroporation and the transformants were then selected on Zeocin-containing plates. The exogenous Sh ble gene has been incorporated into the genome of Schizochytrium according to PCR amplification. More importantly, the majority of the transformants showed similar biomass and total lipid to the wild type strain. Our results suggest that the 18S rDNA is a suitable recombination site and this system could be used to introduce new functional genes into Schizochytrium.