The use of nuclear ribosomal ITS 1 DNA sequences for the identification of Chlorella strains

The Internal Transcribed Spacer I (ITS1) of the nuclear ribosomal DNA of several taxa of Chlorella and of related species of Auxenochlorella, Graesiella, Mychonastes, and Scenedesmus has been sequenced. ITS 1 length ranges from 155 (S. fuscus) to 290bp (both varieties of C. vulgaris), and GC content from 43.1% (S. obliquus) to 63.6% (C. kessleri). ITS 1 length and GC content appear to be at least strain specific. The following clusters of taxa could be recognized: a group composed by C. lobophora and C. vulgaris, a group composed by C. kessleri SAG 211-11 and C. luteoviridis SAG 211-5b as well as larger group composed by the latter four species, wich in turns cluster with C. sorokiniana; a group composed by S. fuscus and S. multiformis, a larger group containing also S. obliquus and, finally, a cluster including the three latter taxa and G. vacuolata, The results obtained in this paper indicate that identification by using ITS 1 is unequivocal at least at species level and in various cases at strain level. The heterogeneity found in ITS 1 sequences of Chlorella probably implies a very ancient separation of the various taxa, which have been kept together taxonomically on the basis of the plesiomorphic overall shape. The ITS 1 sequence data seem a fast and reliable method to classify at the species level strains of Chlorella of uncertain taxonomic position.