Cryptophyceae and rhodophyceae; chemotaxonomy, phylogeny, and application

Abstract The biochemical compositions of seven strains of marine cryptomonad and a rhodophyte were determined in logarithmic phase batch (1.4 L flask) and semi-continuous (10 L carboy) culture. Lipid ranged from 13% to 28%, protein ranged from 53% to 68%, and carbohydrate ranged from 9% to 24% of the organic weight. The major lipid classes in the species examined were polar lipids (78–88% of total lipid). The major sterol in the Cryptophyceae and the Rhodophyceae was 24-methylcholesta-5,22E-dien-3β-ol (62–99% of total sterols); which is also the major sterol in some diatoms and haptophytes. Smaller proportions of cholest-5-en-3β-ol (1–17.7%) were also found in the Cryptophyceae. Most cryptomonads contained high proportions of the n  − 3 polyunsaturated fatty acids (PUFA), 18:3 n  − 3 (20.7–29.9% of the total fatty acids), 18:4 n  − 3 (12.5–30.2%), 20:5 n  − 3 (7.6–13.2%) and 22:6 n  − 3 (6.4–10.8%). However, the blue–green cryptomonad Chroomonas placoidea was characterized by a low proportion of 22:6 n  − 3 (0.2% of total fatty acids), and a significant proportion of 22:5 n  − 6 (4.5%), and the presence of 24-ethylcholesta-5,22E-dien-3β-ol (35.5% of total sterols). The fatty acid composition of the rhodophyte Rhodosorus sp. was similar to those of the Cryptophyceae except for lower proportions of 18:4 n  − 3 and lack of C 21 and C 22 PUFA. It is postulated that the primary endosymbiosis of a photosynthetic n  − 3 C 18 PUFA-producing prokaryote and a eukaryotic host capable of chain elongation and desaturation of exogenous PUFA, resulted in the Rhodophyceae capable of producing n  − 3 C 20 PUFA. The secondary endosymbiosis of a photosynthetic n  − 3 C 20 PUFA-producing eukaryote (such as a Rhodosorus sp. like-rhodophyte) and a eukaryotic host capable of further chain elongation and desaturation, resulted in the Cryptophyceae being capable of producing n  − 3 C 20 and C 22 PUFA de novo. Selected isolates were examined further in feeding trials with juvenile Pacific oysters ( Crassostrea gigas ). Rhodomonas salina CS-24(containing elevated 22:6 n  − 3) produced high growth rates in oysters; equivalent to the microalga commonly used in aquaculture, Isochrysis sp. (T.ISO).