Characterisation ofSkoliomonasgen. nov., a haloalkaliphilic anaerobe related to barthelonids (Metamonada)

Abstract

Metamonads are a large and exclusively anaerobic clade of protists. Additionally, metamonads are one of the three clades with a proposed 'excavate' ancestral cell morphology, characterised by a conspicuous ventral groove often accompanied by a posterior flagellum with a vane. Here, we characterise four isolates of an anaerobic bacterivorous flagellate from hypersaline and alkaline soda lake environments, which represents a novel clade. Small subunit ribosomal RNA (SSU rRNA) gene phylogenies support recent phylogenomic analyses in placing this clade as the sister group toBarthelonaspp., a lineage that is itself sister to or deeply branching within Fornicata (Metamonada). The cells have a distinctive morphology comprised of a hunchbacked cell body with a narrow twisting ventral groove ending in a large opening to a conspicuous cytopharynx curving up the dorsal side of the cell. The right margin of the groove is defined by a thin 'lip' that twists slightly to the left towards the posterior. The posterior of the cell ends in a spike up to half a cell body long. The posterior flagellum bears a wide ventral-facing vane. One isolate forms cysts with a complex wall and a single plug. The narrow ventral groove and elongate cytopharynx are shared with barthelonids. We describe one isolate asSkoliomonas litria, gen. et sp. nov. Further investigation of mitochondrial-related organelles (MRO) inSkoliomonasspp. and detailed ultrastructural studies would be important to understanding the evolution of adaptation to anaerobic conditions in Metamonads—especially fornicates—as well as the evolution of the 'excavate' groove.

Extreme mitochondrial reduction in a novel group of free-living metamonads

“…RCL and Skoliomonas sp. GEMRC (Eglit et al 2024) were maintained in variants of CR media (Gigeroff et al, 2023); Skoliomonas litria in 50 mL of 40 ppt CR with 3% LB, Skoliomonas sp. GEMRC in 50 mL of 40 ppt CR with 1% LB and 3 sterile wheat grains, Skoliomonas sp.…”

“…GEM-RC (GEMRC) and Skoliomonas sp. TZLM3-RCL (RCL) were isolated from sediments of alkaline hypersaline soda lakes (for detailed descriptions see Eglit et al, 2024) (Figure 1A-C). The other two are shallow marine-sediment dwelling ‘barthelonids’ (Yazaki et al 2020): Barthelona sp.…”

“…RCL (C), as well as Barthelona sp. PCE (D) showing overall morphology (imaging and methods described in Eglit et al 2024). Scale bars indicate a length of 10 µm.…”