SYSTEMATICS, BIOLOGICAL CHARACTERISTICS AND POTENTIAL APPLICATION OF EUSTIGMATOPHYCEAE

The Eustigmatophyceae was segregated from the Xanthophyceae according to the cytological and ultrastructural properties by Hibberd Leedale in 1970 and 1971. At present, it includes one order, six families, thirteen genera, and about thirty species. The major photosynthetic pigments of the Eustigmatophyceae are chlorophyll a, violaxanthin, vaucheriaxanthin, -carotene, and carotene-ester. The cells possess a parietal lobed chloroplast or several discoid chloroplasts. The pyrenoid with a narrow stalk presents only in the vegetative cells. The chloroplast contains three-thylakoid lamellae and no girdle lamellae. The chloroplast is surrounded by a double-membrane envelope and then a layer of endoplasmic reticulum that is not continuity with the nuclear envelope. There is a large spheroidal vacuole with lots of vibrating granular contents and a conspicuous reddish globule in the cytoplasm. In general, eustig-matophytes are reproduced by the formation of autospores. The larger spherical species produce either two D-shaped or four tetrahedral autospores. Eight or sixteen autospores sometimes were observed in the mother cell. Most species can produce lageniform zoospores. The zoospores in most species produce only one emerge flagellum with tubular mastigonemes laterally while others degenerate. In biflagellate species, the second flagellum is short, posteriorly directed and smooth. The relationship between the Eustigmatophyceae and other Heterokontophyta was established by the 18S rDNA and rbcL gene sequence analysis. Fatty acid analysis showed that the Eustigmatophyceae contained eicosapentaenoic acid (EPA). The eustigmatophytes distribute widely in the freshwater bodies, seawater and soil surface. Several species of Nannochloropsis are widely used as aquacultural feeds for rotifer, artemia and larvae of marine fishes, prawns and crabs, and many species are potential producers of EPA and carotenoids. In addition, many species of the Eustigmatophyceae are rich in oil, so they are the potential source for biofuels production.