Ultrastructural and molecular characterization of Tetraselmis strains (Chlorodendrophyceae, Chlorophyta) isolated from Chile

Abstract

Species of the genus Tetraselmis (Chlorodendrophyceae, Chlorophyta) have traditionally been used in aquaculture facilities as food for
larval varieties of marine organisms. Recently, some strains with high lipid content have been considered as having potential for biofuel
production. Although many Tetraselmis species are relatively well-characterized using light and electron microscopical methods,
there are still taxonomic ambiguities among the species. DNA sequence analysis, which provides a reliable and more convenient tool
for species delimitation, has been poorly used in Tetraselmis. In this study, three strains of Tetraselmis, isolated from coastal Chilean
waters, have been characterized using an integrative approach (light and electron microscopy, molecular phylogeny of ITS, including
secondary structure analysis). According to the pyrenoid ultrastructure of the strains investigated two of them (from Dichato and
Coliumo) belong to the subgenus Parviselmis, while the Caldera strain corresponds to the subgenus Tetrathele. Even though it was not
possible to identify the strains at species level, it was clearly demonstrated by phylogenetic analyses of ITS-1 and ITS-2 sequences
and by ITS-2 secondary structure that the Dichato and Coliumo strains are the same species, and could belong either to T. suecica or T.
chui. However, the Caldera strain might correspond to an undescribed species. As our study has shown, the genus Tetraselmis needs to
be taxonomically revised using an integrative approach, which includes the investigations of authentic strains of this genus.