Biological properties and biomass culture of the microalgae chaetoceros muelleri from Giao Thuy mangrove for use in aquaculture

A Chaetoceros strain was successfully isolated to a unialgal state from Giao Thuy mangrove and identified to be of Chaetoceros muelleri species based on morphological properties and 18S rDNA sequence analysis. ASW medium together with 250/00 of salinity was found to be best suitable for the growth of this strain and was applied to its biomass production.
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Biological properties and biomass culture of the microalgae chaetoceros muelleri from Giao Thuy mangrove for use in aquaculture JOURNAL OF SCIENCE OF HNUE Natural Sci., 2010, Vol. 55, No. 6, pp. 141-148 BIOLOGICAL PROPERTIES AND BIOMASS CULTURE OF THE MICROALGAE Chaetoceros muelleri FROM GIAO THUY MANGROVE FOR USE IN AQUACULTURE Le Thi Phuong Hoa(∗) Hanoi National University of Education Nguyen Thi Hoai Ha, Pham Thi Bich Dao Vietnam National University, Hanoi Nguyen Ngoc Tuyen Hanoi Open University (∗) E-mail: lephhoa@yahoo.com Abstract. A Chaetoceros strain was successfully isolated to a unialgal state from Giao Thuy mangrove and identified to be of Chaetoceros muelleri species based on morphological properties and 18S rDNA sequence anal- ysis. ASW medium together with 250/00 of salinity was found to be best suitable for the growth of this strain and was applied to its biomass produc- tion. The fatty acid profile of C. muelleri strain was typical of most diatoms with the exception of low level of 16:0 and 14:0 acids. This strain possessed high concentration of polyunsaturated fatty acids (PUFAs), 36.64% total fatty acids, which is much higher than that of C. calcitrans, C. gracilis and C. muelleri in previous reports. Among these acids, eicosapentaenoic acid (EPA) and arachidonic acid (AA) had significant proportion (24.76% and 7.84%, respectively), which are also higher than the above strains. The iso- lated C. muelleri strain represents a high-quality food resource and has a high potential for use in aquaculture. Keywords: Chaetoceros muelleri, mangrove microalgae, fatty acid, aqua- culture1. Introduction Microalgae constitutes major oceanic and freshwater primary producers andhave been utilized by man for hundreds of years from human and animal nutrition,cosmetics to therapeutic purposes. They possess high-value compounds such aspolyunsaturated fatty acids (PUFAs), carotenoids, proteins, polysaccharides andvitamins [8, 11]. In aquaculture, microalgae play a crucial role as they are thenatural food source for many marine animals. Their consumers include bivalve 141Le Thi Phuong Hoa, Nguyen Thi Hoai Ha, Pham Thi Bich Dao and Nguyen Ngoc Tuyenmollusks (e.g. abalones, oysters, scallops, clams and mussels) at all growth stages,crustaceans and some fish species at the larval and early juvenile stages as wellas zooplankton which is widely used in aquaculture food chains [2, 8, 11, 13]. Tobe applied in aquaculture, microalgae have to meet various criteria. They needto be of appropriate size and shape for ingestion. They must have rapid growthrates and be easy to culture and be nontoxic. Finally, they must be nontoxic andhave a good nutrient composition, including high protein content, high level of longchain polyunsaturated fatty acids (PUFAs) such as eicosapentaenoic acid (EPA),arachidonic acid (AA) and docosahexaenoic acid (DHA) [2, 8, 11]. Some fattyacids are indeed essential for many marine animals and required for the growth andmetamorphosis of many larvae [11-13]. Over the last four decades, several hundredmicroalgae species have been tested as food, but a limited number have gainedwidespread use in aquaculture [2]. Strains of Chaetoceros genus are used to feed different groups of commerciallyimportant aquatic organisms, including penaeid shrimp larvae, bivalve mollusk lar-vae and postlarvae, prawn larvae and brine shrimp [2]. C. calcitrans and C. gracilisare of the most frequently used species in commercial mariculture operations. Inthis study, a Chaetoceros strain was isolated from a special ecosystem, mangroveforest, evaluated its nutritional value through fatty acid composition, and suitablegrowth conditions were built up aiming for potential application in Mariculture.2. Content2.1. Material and Methods * Selection, isolation and identification of Chaetoceros muelleri. Samples were collected from different sites of the Giao Thuy Mangrove Forest.Microalgae were grown in medium f/2 at room temperature and illuminated withneon lights (Philips daylight tubes) on 10:14 h light: dark cycles. Chaetocerosstrains were isolated to a unialgal state based on their morphological properties [10].Pictures were taken under 1000-fold OLYMPUS CX41 microscopy. Total DNA wasextracted thereafter and 18S rDNA-coding region were amplified according to Fawleyand Fawley [3]. PCR products were directly sequenced in an ABM Prism 3100-AvantSequencer. The obtained sequences were aligned randomly with sequences on NCBIdatabase by BLAST tool to get the positive identity. * Culture conditions of Chaetoceros muelleri. C. muelleri was cultured in different medias f/2, ASW, ESM, Walne and f/2without silicon [6] in 150 mL unaerated flasks. Cells were harvested every two daysand counted in a Neubauer haemocytometer in three replicates. Medium providingbest growth of algal cells was chosen for biomass culture of C. muelleri. Effect of142 Biological properties and biomass culture of the microalgae Chaetoceros muelleri...salinity to the growth of C. muelleri was also examined with different levels from00/00 to 400/00 NaCl in ASW medium. * Determination of fatty acid composition. Biomass for fatty acid analysis of C. muelleri was obtained from continuouslyaerated culture suspensions in 1 litre plastic containers. Cells were harvested atthe early stationery phase by continuous centrifugation at 10,000 rpm, at 40 C in15 min and extracted thereafte ...