Biochemical taxonomy and molecular phylogeny of the genus Chlorella sensu lato (Chlorophyta)

A multimethod approach was used to characterize unicellular green algae tha t were traditionally assigned to the genus Chlorella Beijerinck and to reso lve their phylogenetic relationships within the Chlorophyta. Biochemical, p hysiological, and ultrastructural characters, together with molecular data such as DNA base composition and DNA hybridization values, were compared wi th a molecular phylogeny based on complete 18S rRNA sequences. Our results show that Chlorella taxa are dispersed over two classes of chlorophytes, th e Trebouxiophyceae and the Chlorophyceae. We propose that only four species should be kept in the genus Chlorella (Chlorophyta, Trebouxiophyceae): C. vulgaris Beijerinck, C. lobophora Andreyeva, C. sorokiniana Shih, et Krauss , and C. kessleri Fott et Novakova. Common characteristics of these taxa ar e glucosamine as a dominant cell wall component and the presence of a doubl e thylakoid bisecting the pyrenoid matrix. Norspermine, norspermidine, and secondary carotenoids are never produced. Other "Chlorella" species belong to different taxa within the Trebouxiophyceae ("C." protothecoides = Auxeno chlorella protothecoides [Kruger] Kalina et Puncocharova, "C." ellipsoidea, "C." mirabilis, "C." saccharophila, and "C." luteoviridis) and Chlorophyce ae ("C." zofingiensis and "C." homosphaera = Mychonastes homosphaera Kalina et Puncocharova). The latter taxa can easily be recognized by the producti on of secondary carotenoids under nitrogen-deficient conditions.