STUDY ON BIOLOGICAL CHARACTERISTICS OF HETEROTROPHIC MARINE MICROALGA—SCHIZOCHYTRIUM MANGROVEI PQ6 ISOLATED FROM PHU QUOC ISLAND, KIEN GIANG PROVINCE, VIETNAM 1 Dang Diem Hong, 2 Hoang Thi Lan Anh, and Ngo Thi Hoai Thu Institute of Biotechnology, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet Road, Cau Giay, Hanoi, Vietnam 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 maxi- mize 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 accumula- tion 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 Æ mL )1 , 23.7 g Æ L )1 , 38.56% of DCW, and 8.71 g Æ L )1 (in 5 L fermenter), respec- tively, and 49.71 · 10 6 cells Æ mL )1 , 25.34 g Æ L )1 , 46.23% of DCW, and 11.55 g Æ L )1 (in 10 L fermen- ter), respectively. Biomass of PQ6 strain possessed high contents of Na, I, and Fe (167.185, 278.3, and 43.69 mg Æ 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. Key index words: aquaculture; docosahexaenoic acid; eicosapentaenoic acid; heterotrophic marine algae; polyunsaturated fatty acid Abbreviations: ASW, artificial seawater; DCW, dry cell weight; DHA, docosapentaenoic acid; EPA, eicosapentaenoic acid; GPY medium, medium without chloramphenicol; GPYc medium, medium with glucose, polypepton, yeast extract, and chl- oramphenicol; PQ, Phu Quoc; PUFA, polyunsat- urated fatty acid; TFA, total fatty acid Polyunsaturated fatty acids (PUFAs), which are precursors for synthesis of signaling molecules such as prostaglandins, thromboxanes, and leukotrienes, are important components of cell membrane phos- pholipids and play an important role in the preven- tion or treatment of a variety of diseases, such as arteriosclerosis, thrombosis, arthritis, and several types of cancer (Funk 2001, Qiu 2003, Damude and Kinney 2007). Among the PUFAs, DHA is interesting for research and application. Numerous clinical studies have demonstrated that DHA is essential for proper visual and neurological development of infants as well as the mental health of adults (Willatts and Forsyth 2000, Iribarren et al. 2004). It is also involved in the prevention of cardiovascular and neurological diseases (Simopoulous 1999, Kris-Etherton et al. 2002, Cole et al. 2005). For this reason, food manufacturers often fortify infant food products, drugs, and animal feeds, among others, with DHA (Gantar and Svircev 2008, Raghukumar 2008). Fish oil, being the traditional source of n-3 PUFAs such as DHA and EPA, has already been extensively researched since 1980. However, fish oil has disadvantages in terms of odor, taste, stability, and the possibility of contamination with heavy metals, dioxin, and polychlorinated biphenyl (PCBs) (Raghu- kumar 2008). Because of this, the demand for alter- native naturally occurring fats and oils containing these fatty acids has increased. Marine microorgan- isms, such as species of dinoflagellates and heterotro- phic microalgae, contribute significant amounts of DHA in the marine food chain and hence are charac- terized as ‘‘de novo’’ producers of DHA. As a result, DHA is now commercially produced from Crypthecodi- nium cohnii, a marine dinoflagellate, and thraustochy- trid Schizochytrium, formerly considered a fungus but reclassified to the Labyrinthulomycetes of the king- dom Stramenopila (Porter 1990, Archibald and Keel- ing 2004, Inouye 2004, Ward and Singh 2005, Raghukumar 2008). Schizochytrium sp. is a marine microalga that has been developed as a commercial source of DHA. Biomass densities of some strains can reach 200 g Æ L )1 in short fermentation times of 90–100 h under glucose and nitrogen-fed batch culture and can also accumulate up to 40–45 g Æ L )1 DHA (Bailey et al. 2003). Dried biomass of Schizochytrium is recognized to be generally safe (GRAS) for use as 1 Received 13 April 2010. Accepted 2 February 2011. 2 Author for correspondence: e-mail ddhong60vn@yahoo.com. J. Phycol. 47, 944–954 (2011) Ó 2011 Phycological Society of America DOI: 10.1111/j.1529-8817.2011.01012.x 944