Expanding the molecular and morphological diversity of Apusomonadida, a deep-branching group of gliding bacterivorous protists

Abstract

AbstractApusomonads are cosmopolitan bacterivorous biflagellate protists usually gliding on freshwater and marine sediment or wet soils. These nanoflagellates form a sister lineage to opisthokonts and may have retained ancestral features helpful to understanding the early evolution of this large supergroup. Although molecular environmental analyses indicate that apusomonads are genetically diverse, few species have been described. Here, we morphologically characterize eleven new apusomonad strains. Based on molecular phylogenetic analyses of the rRNA gene operon, we describe four new strains of the known speciesMultimonas media, Podomonas capensis, Apusomonas proboscideaandApusomonas australiensis, and renameThecamonas oxoniensisasMylnikovia oxoniensisn. gen., n. comb. Additionally, we describe four new genera and six new species:Catacumbia lutetiensisn. gen. n. sp.,Cavaliersmithia chaoaen. gen. n. sp.,Singekia montserratensisn. gen. n. sp.,Singekia franciliensisn. gen. n. sp.,Karpovia croatican. gen. n. sp. andChelonemonas dolanin. sp. Our comparative analysis suggests that apusomonad ancestor was a fusiform biflagellate with a dorsal pellicle, a plastic ventral surface and a sleeve covering the anterior flagellum, that thrived in marine, possibly oxygen-poor, environments. It likely had a complex cell cycle with dormant and multiple fission stages, and sex. Our results extend known apusomonad diversity, allow updating their taxonomy, and provide elements to understand early eukaryotic evolution.