THE BIOCHEMICAL-COMPOSITION OF MARINE MICROALGAE FROM THE CLASS EUSTIGMATOPHYCEAE

The biochemical composition of four strains of microalgae from the class Eustigmatophyceae was determined to assess their usefulness as live feeds for mariculture and to establish characteristic features for use in chemotaxonomic studies. We studied Nannochloropsis salina (strain CS-190)from Scotland, two strains of Nannochloropsis oculata (CS-179 and CS-216) from Japan, and an unnamed eustigmatophyte (CS-246) isolated from Queensland waters that appears to be closely related to N. oculata. Gross compositional features were similar: total carbohydrate ranged from 5.2% (N. oculata CS-179) to 8.9% (N. salina) of cell dry weight. Polysaccharide comprised 74% (N. oculata CS-179) to 88% (CS-246) of this total. Glucose was the principal polysaccharide sugar (45.2-66.2% of total sugars). Other sugars included fucose, galactose, mannose, rhamnose, ribose, and xylose (2.0-14.0%). Arabinose was a minor constituent in all species (0.6-1.7%). Protein varied from 17.8% (N. salina) to 22.1% (N. oculata CS-216) of the cell dry weight. The major amino acids were arginine, glutamate, and aspartate (7.2-10.4% of total amino acids), with methionine, cystine, histidine, tryptophan, hydroxy-proline, ornithine, and gamma-aminobutyric acid much less abundant (0.03-2.6%). Lipid content ranged from 8.2% (N. oculata CS-216) to 16.9% (N. salina) of cell dry weight, the latter value reflecting enhanced concentrations of triacylglycerols in N. salina. The major fatty acids were palmitic acid (16:0), palmitoleic acid [16:1(n-7)], and eicosapentaenoic acid [20:5(n-3)] with lesser amounts of lauric acid (14:0), linoleic acid [18:2(n-6)], and others. The sterols consisted almost entirely of cholesterol, which is an essential constituent Of crustacean diets. Chlorophyll a ranged from 0.6% (N. oculata CS-216) to 1.7% (N. oculata CS-179 and N. salina) of cell dry weight. Chlorophylls b and c were not detected. All strains contained a characteristic Pattern of carotenoid pigments, which included violaxanthin, beta-carotene, zeaxanthin, and a pigment tentatively identified as vaucheriaxanthin-ester. The distinctive pigment and lipid compositional data can be used as chemotaxonomic markers for Nannochloropsis and for assigning microalgae to the class Eustigmatophyceae. Nannochloropsis oculata is widely used as an algal feed in mariculture, and based on the similarity of the biochemical data, both N. salina and the unnamed tropical species should also prove to be nutritionally valuable live algal feedstocks. Feeding trials will be needed to confirm this.