Cultivation of Ancyromonas melba, and Reclassification as the Type Species of Divimonas gen. nov., a Phylogenetically Important Ancyromonad Lineage

Ancyromonadida is a taxon of small heterotrophic flagellates occupying an unresolved but deep-branching position in the eukaryotic tree of life, thus suspected to be important to studies of early eukaryotic evolutionary relationships and the characteristics of the last eukaryotic common ancestor. Sampling and cultivation of the full diversity of ancyromonad species are therefore areas of considerable interest. Ancyromonas melba is a species originally described from hypersaline material for which no monoprotistan culture or molecular data have been available, but whose distinct morphology suggests it may represent a new major lineage within Ancyromonadida. We report the first cultivation of this morphospecies in hypersaline media, with characterization including scanning electron microscopy and small subunit rRNA gene sequencing. Distinguishing morphological features include the predominantly ventral placement of the ventral groove, the approximately equal thickness of the anterior and posterior flagella, and the relatively long anterior flagellum. Phylogenetic analysis shows that the isolate does not branch within Ancyromonas or any other currently described genus of Ancyromonadida, but represents a novel genus-level lineage, the position of which within ancyromonads could not be robustly inferred. We therefore propose a new genus for this species and rename it Divimonas melba n. gen., n. comb.