Abstract
BackgroundPhotosynthetic eukaryotes with a secondary plastid of red algal origin (cryptophytes, haptophytes, stramenopiles, dinoflagellates, and apicomplexans) are hypothesized to share a single origin of plastid acquisition according to Chromalveolate hypothesis. Recent phylogenomic analyses suggest that photosynthetic “chromalveolates” form a large clade with inclusion of several non-photosynthetic protist lineages. Katablepharids are one such non-photosynthetic lineage closely related to cryptophytes. Despite their evolutionary and ecological importance, katablepharids are poorly investigated.Methodology/Principal FindingsHere, we report a newly discovered flagellate, Roombia truncata gen. et sp. nov., that is related to katablepharids, but is morphologically distinct from othermembers of the group in the following ways: (1) two flagella emerge from a papilla-like subapical protrusion, (2) conspicuous ejectisomes are aligned in multiple (5–11) rows, (3) each ejectisome increases in size towards the posterior end of the rows, and (4) upon feeding, a part of cytoplasm elastically stretch to engulf whole prey cell. Molecular phylogenies inferred from Hsp90, SSU rDNA, and LSU rDNA sequences consistently and strongly show R. truncata as the sister lineage to all other katablepharids, including lineages known only from environmental sequence surveys. A close association between katablepharids and cryptophytes was also recovered in most analyses. Katablepharids and cryptophytes are together part of a larger, more inclusive, group that also contains haptophytes, telonemids, centrohelids and perhaps biliphytes. The monophyly of this group is supported by several different molecular phylogenetic datasets and one shared lateral gene transfer; therefore, we formally establish this diverse clade as the “Hacrobia.”Conclusions/SignificanceOur discovery of R. truncata not only expands our knowledge in the less studied flagellate group, but provide a better understanding of phylogenetic relationship and evolutionary view of plastid acquisition/losses of Hacrobia. Being an ancestral to all katablepharids, and readily cultivable, R. truncata is a good candidate for multiple gene analyses that will contribute to future phylogenetic studies of Hacrobia.
Highlights
Katablepharids are cosmopolitan colorless flagellates that play an important role as predators in both marine and freshwater microbial ecosystems [1,2,3,4,5,6]
A close relationship between katablepharids and cryptophytes is clear, whether or not they are one another’s closest relatives remains open to debate; several other lineages previously classified as incertae sedis have been shown to branch in this part of the eukaryotic tree in molecular phylogenetic analyses, such as telonemids [12,13] andbiliphytes, known only from environmental sequences and fluorescence in situ hybridization (FISH) images [14,15,16,17]
Our molecular phylogenetic analyses consistently showed R. truncata is the sister to all hitherto known katablepharids within an emerging group of great diversity, the Hacrobia
Summary
Katablepharids are cosmopolitan colorless flagellates that play an important role as predators in both marine and freshwater microbial ecosystems [1,2,3,4,5,6]. A close relationship between katablepharids and cryptophytes is clear, whether or not they are one another’s closest relatives remains open to debate; several other lineages previously classified as incertae sedis have been shown to branch in this part of the eukaryotic tree in molecular phylogenetic analyses, such as telonemids [12,13] and (pico)biliphytes, known only from environmental sequences and fluorescence in situ hybridization (FISH) images [14,15,16,17]. Despite their evolutionary and ecological importance, katablepharids are poorly investigated
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
