HIGH-YIELD MIXOTROPHIC CULTURES OF THE MARINE MICROALGA TETRASELMIS-SUECICA (KYLIN) BUTCHER (PRASINOPHYCEAE)

The effects of three organic compounds were tested on one of the most used marine micro-algae in the aquaculture of molluscs and crustaceans, Tetraselmis suecica. Studies were made in axenic conditions with yeast extract, peptone and glucose added to the culture medium, each alone, in combinations of two or all together. Medium without any organic compound was used for the control. Cultures containing yeast extract grew best, reaching maximum cell density of 3.79 x 10(6) and 3.84 x 10(6) cells ml-1. The organic carbon source affected the biochemical composition. The components most affected were the carbohydrates, with values between 6.5 pg cell-1 in control cultures and 48.5 pg cell-1 in glucose cultures. Protein content ranged between 27.5 pg cell-1 in control cultures and 88.6 pg cell-1 in yeast + glucose + peptone cultures. The lipid content changed little. Maximum protein yields were reached in cultures with yeast + glucose and with yeast + glucose + peptone, with values of 24.6 and 28.2 mg l-1 d-1 respectively. These values are 22 and 25 times those in control cultures. A maximum carbohydrate yield of 7.9 mg carbohydrate per litre per day was obtained in yeast + glucose + peptone cultures, 27 times that in the control cultures. The maximum lipid yield was obtained with yeast + glucose + peptone and yeast + glucose. Maximum energy values were 308 kcal l-1 in yeast extract + glucose + peptone cultures and 279 kcal l-1 in yeast extract + glucose cultures. Gross energy values in control cultures were 24.5 kcal l-1, but peptone cultures presented the minimum energy value, 22 kcal l-1. The yeast extract: glucose ratio in the culture medium was optimized. A ratio 2:1 produced the best yields in cells, protein, carbohydrate and gross energy.