A New Genus of Filamentous Cyanobacteria, Dgebuadzia, from a Volcanic Lake in Northern Mongolia

This study analyzes the diversity of thin filamentous cyanobacteria from the volcanic Lake Terkhiin-Tsagaan, Mongolia. We isolated and characterized two strains from benthic samples collected from the lake. Using light microscopy, phylogenetic analysis of 16S rRNA gene sequences, and examination of the secondary structures of the 16S–23S ITS helices, we describe a new genus, Dgebuadzia, and a new species, Dgebuadzia mongoliensis. The 16S rRNA gene similarity to Phormidesmis was below the genus-level threshold (89.5% to P. mollis NIES-2126; minimum 94.19% to non-mollis Phormidesmis species), and the strains formed a well-supported monophyletic clade (BI/ML = 1/100) that is distinct from all other Leptolyngbyaceae included in the analysis. The strains also differed from Phormidesmis in the secondary structure of the Box-B and V3 helix. The new genus is closely related to P. arctica, a taxon whose original description is nomenclaturally invalid and which therefore cannot be formally transferred, although its phylogenetic position places it within the Dgebuadzia lineage. The data presented here contribute to our understanding of the diversity of thin filamentous cyanobacteria and expand current knowledge of the algal flora of Mongolian volcanic lakes.