A New Halophilic Heterolobosean Flagellate, Aurem hypersalina gen. n. et sp. n., Closely Related to the Pleurostomum-Tulamoeba Clade: Implications for Adaptive Radiation of Halophilic Eukaryotes

Halophilic protozoa are independently scattered across the molecular phylogeny of eukaryotes; most of which are assigned to Heterolobosea. Here, we isolated a biflagellate from a hypersaline water of 342‰ salinity. This isolate shared several morphological features with typical halophilic heterolobosean flagellates. In addition, molecular phylogenetic trees of the 18S rRNA gene sequences clearly indicated flagellate is a heterolobosean species closely related to the halophilic Tulamoebidae. However, the flagellate was not accommodated to any described genus. Cells were ovoid-shaped, and no amoebae were observed. The two unequal flagella beat heterodynamically. An ear-like bulge at the margin of a cytostomal groove was observed. Flagellates could grow at 100–200‰ salinity, suggesting an obligately halophilic species. Currently, it appears that the new halophilic Aurem hypersalina forms a strong clade with Tulamoebidae, and is sister to the Tulamoebidae, indicating that this new clade is composed almost entirely of obligate halophilic taxa. Thus, A. hypersalina and the Tulamoebidae clade currently represent a unique adaptive radiation of halophilic eukaryotes.