Phylogenetic analysis of cyanidian algae (Cyanidiales, Rhodophyta), using 18S rRNA gene sequences

Summary : Cyanidian algae were collected from 54 hot springs in Japan. These algae were identified as three species; Cyanidium caldarium, Galdieria sulphuraria and G.maxima based on their morphology under the culture conditions. To elucidate the phylogenetic relationship among these algae, molecular phylogenetic analysis of the 18S rRNA gene was carried out using 11 strains selected from our collection and 7 strains from the other culture collections. The morphological features of Galdieria partita from the USA and G.daedala were similar to G.sulphuraria under the same culture condition. On the other hand, Galdieria partita from Russia was similar to G.maxima. A phylogenetic tree revealed the monophyly of Cyanidium and Galdieria, and the latter was divided into three clades; G.maxima + G.partita from Russia, G.sulphuraria + G.partita from the USA and G.sulphuraria + G.daedala. Based on their cell size, number of endospores and chloroplast numbers per cell, C.caldarium and G.maxima can be distinguished. In contrast, it is hard to distinguish morphologically the two phylogenetic groups of G.sulphuraria. At present, we believe it is appropriate to place them in G.sulphuraria until morphological differences are discovered between them. Key words : 18S rRNA gene, Cyanidium caldarium, Galdieria daedala, Galdieria maxima, Galdieria partita, Galdieria sulphuraria, phylogeny