Aquaculture 159 ( 1997) Ill123
Changes in the nutrient composition of Tetraselmis suecica cultured semicontinuously with different nutrient concentrations and renewal rates
Ana Otero, Jaime Fgbregas
Departamrnto de Microbiologfa, Facultad de Farmacia,
Unicersidad de Santiago, Santiago 15706,
Accepted 8 September 1997
Abstract The marine microalga Tetraselmissuecica was cultured semicontinuously with two nutrient concentrations: 2 and 4 mmol N I-’ and five rates of daily renewal of the culture media in the range IO-50%, in order to study the changes in the nutrient composition of the cells produced under such conditions. An increase in the renewal rate produced an increase in protein and lipid content of the biomass to the detriment of carbohydratecontent, the only fraction accumulated by T. suecica as energetic reserve under nitrogen deficient conditions. Cellular content of these three fractions did not accurately reflect the relative composition, since total organic content of the cells decreased with increasing renewal rates attenuating the increase in protein and lipid contents. As a result, cell caloric content remained almostconstant. The degree of unsaturation of fatty acids increased with increasing renewal rate, with a two-fold increase of the percentage of total n - 3 fatty acids. On the other hand, the percentage of eicosapentaenoic acid (EPA) decreased with increasing renewal rate indicating a different control of the metabolism of this long-chain polyunsaturated fatty acid in T. suecica. Results demonstrate theefficiency of the use of the semicontinuous culture technique for the production of microalgal biomass of optimal biochemical composition being especially useful for the study of the nutritional requirements of filter-feeding marine organisms. 0 1997 Elsevier Science B.V.
Keywords: Tetrasrlmis suecica; Continuous culture; Biochemical composition; Protein; Lipid; Carbohydrates;
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A. Otero, .I. Fribregas/Aquaculture
159 (19971 III-123
1. Introduction Microalgae are the basis of the trophic chain in most aquaculture systems, the development of efficient production systems ofalgal biomass of optimal biochemical quality being a key point for the reduction of labour costs and the improvement of growth and survival of the higher links of the trophic chain. For such purpose, the use of continuous culture techniques, providing biomass of stable biochemical composition with productivities much higher than batch cultures seems to be optimal. Continuous cultures have beenextensively used in ecological studies of phytoplankton growth and composition in response to different types of limitation (Droop, 19831, but these studies are of little value for aquaculture applications, since they were carried out at cell densities much lower than those required for mass production. Several authors have designed and tested different culture systems for the continuous production ofmicroalgal biomass, but most of these studies have been focused on the optimisation of biomass production, paying little attention to the nutrient composition of the biomass generated (Spectorova et al., 1981/1982; Laing and Jones, 1988, Richmond et al., 1993). The use of continuous cultures of marine microalgae to study the nutritional requirements of marine organisms was first suggested in thepioneer works of Scott (1980) and Taub (1980), indicating the potential of these systems to generate microalgal biomass of optimal nutritional quality. Despite the feasibility of the manipulation of algal composition in continuous cultures was confirmed later (Sukenik and Wahnon, 1991; Sukenik et al., 1993), these techniques have not been applied extensively, mainly due to the difficulties of...