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Abstract

The genus Pyramimonas Schmarda was traditionally described on observations of its periplast and internal structure of different flagellar apparatus or eyespot orientations and currently comprises of ca. 60 species that are divided into six subgenera: Pyramimonas, Vestigifera, Trichocystis, Punctatae, Hexactis, and Macrura. In order to understand the genetic diversity and phylogenetic relationships of genus Pyramimonas members, we analyzed nuclear SSU rDNA molecular data from 41 strains isolated from different locations of the Ryukyu Archipelago. Phylogenetic analyses revealed that strains could be segregated into six clades, four of which represented existing subgenera: Pyramimonas, Vestigifera McFadden, Trichocystis McFadden, and Punctatae McFadden, and two undescribed subgenera. Most recovered subgenera were represented by established and confirmed species of Pyramimonas along with several potentially undescribed species with the exception of one undescribed subgenus. Many of the newly isolated strains were closely related with Pyramimonas aurea and P. olivacea, and were considered to belong to subgenus Punctatae. However, nuclear SSU rDNA phylogenetic trees clearly showed that they are genetically different and can be divided into two subgenera. Subgenus Punctatae comprised of Pyramimonas olivacea and related strains whilst, P. aurea and related strains belonged to an undescribed subgenus which is tentatively referred to as undescribed subgenus 1 which shared a sister-group relationship with subgenus Punctatae. The genetic similarity based on nuclear SSU rDNA ranged from 98.2% to 99.9% and 97.3% to 98.3% within and between subgenera, respectively. The present work shows high level of genetic diversity for the genus Pyramimonas from the Ryukyu Archipelago, Japan.

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