Abstract
We report a novel nanoflagellate, Ophirina amphinema n. gen. n. sp., isolated from a lagoon of the Solomon Islands. The flagellate displays ‘typical excavate’ morphological characteristics, such as the presence of a ventral feeding groove with vanes on the posterior flagellum. The cell is ca. 4 µm in length, bears two flagella, and has a single mitochondrion with flat to discoid cristae. The flagellate exists in two morphotypes: a suspension-feeder, which bears flagella that are about the length of the cell, and a swimmer, which has longer flagella. In a tree based on the analysis of 156 proteins, Ophirina is sister to jakobids, with moderate bootstrap support. Ophirina has some ultrastructural (e.g. B-fibre associated with the posterior basal body) and mtDNA (e.g. rpoA–D) features in common with jakobids. Yet, other morphological features, including the crista morphology and presence of two flagellar vanes, rather connect Ophirina to non-jakobid or non-discobid excavates. Ophirina amphinema has some unique features, such as an unusual segmented core structure within the basal bodies and a rightward-oriented dorsal fan. Thus, Ophirina represents a new deeply-branching member of Discoba, and its mosaic morphological characteristics may illuminate aspects of the ancestral eukaryotic cellular body plan.
Highlights
The origin of eukaryotes, and their subsequent early diversification into major extant lineages, are each fundamentally important yet challenging topics in evolutionary biological studies
We formally describe strain JB as Ophirina amphinema gen. et sp. nov., and place it within a new suborder of Jakobida
Strain JB exhibited dimorphism under our growth conditions
Summary
The origin of eukaryotes, and their subsequent early diversification into major extant lineages, are each fundamentally important yet challenging topics in evolutionary biological studies. The diversity within the order Jakobida is known to be undersampled: a recent study based on environmental sequences showed that a large number of jakobids remain to be cultured[13]. Given the possibility that the discobids may be an early-diverging lineage of eukaryotes, currently-unidentified members of the group may hold key information for considering the early evolution of Discoba, and of all eukaryotes. The identification of such novel discobids has been a much-anticipated protistological subject. We sequenced the complete mitochondrial genome of O. amphinema for the present study, and discuss parallel losses of mitochondrial genes within Jakobida
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