A Deeply Branching Lineage in Heterolobosea (Discoba) With Multiflagellated and Multigrooved Life Stages

Abstract

Several distantly related, deep-branching lineages within the eukaryotic tree of life share what is known as the “typical excavate” morphology. This cell architecture includes a suspension-feeding ventral groove, supported by complex and specific structures of the cytoskeleton, and a vane-bearing posterior flagellum. Within Discoba, such characteristics were found only in the deepest branch, Jakobida, also famous for having the most gene-rich and bacterial-like mitogenomes. Some members of the discoban lineage Heterolobosea also possess a ventral groove. However, they lost many other typical excavate characteristics, including the flagellar vane and some flagellar root elements. We have established a clonal culture of a free-living freshwater flagellate from Malaysia, strain NY0229, described here under the provisional name Multisulcus malaysiensis nom. prov. Electron microscopy observations show a conspicuous ventral groove reinforced with microtubules of the flagellar apparatus and a vane on the posterior flagellum. Strain NY0229 has typical excavate biflagellated forms but also exhibits very atypical multiflagellated and multigrooved forms. The kinetid consists of two orthogonally oriented kinetosomes; both flagella of biflagellate cells display proximal and distal projections. Molecular phylogenetic analyses support a deep-branching position of the new strain within Heterolobosea, as the sister lineage to all previously known Eutetramitia.