Fottea X:X | DOI: 10.5507/fot.2025.012

Parabrasilonema hainanensis gen. et sp. nov. (Scytonemataceae, Nostocales), a novel filamentous cyanobacterium isolated from a tropical reservoir in China

Qi Zhang1, 2, Lin Li3, Tianli Li2, Lingling Zheng2, Lirong Song2
1 Key Laboratory of Lake and Watershed Science for Water Security, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China;
2 National Aquatic Biological Resource Center, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China
3 Key Laboratory of Algal Biology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China

A filamentous, heterocytous cyanobacterial strain FACHB-3638 was isolated from Yongzhuang Reservoir, a tropical drinking water reservoir on Hainan Island, southern China. This cyanobacterium formed macroscopic, felt-like mats on submerged concrete substrates, covering extensive areas of the shallow riverbed. The filaments were isopolar, cylindrical, and nearly straight or flexuous, exhibiting infrequent scytonematoid false-branching and producing firm, often layered and colored sheaths. Morphologically, the strain resembles members of the Scytonemataceae family, particularly Brasilonema, but phenotypically differed from other scytonematoid genera in thallus form, branching pattern, trichome structure, heterocyte positioning, and habitat preference. Phylogenetic analyses based on 16S rRNA gene sequences placed this strain in a clade distinct from closely related genera within the family Scytonemataceae. The 16S rRNA sequence of this strain shared less than 95% genetic identity with currently described Scytonemataceae genera. Based on a polyphasic approach including data on morphology, ultrastructure, ecology, 16S rRNA phylogeny and secondary structure, we propose Parabrasilonema hainanensis gen. et sp. nov. as a new cyanobacterial taxon. Additionally, phylogenetic analyses showed that strain FACHB-3638, along with uncultured cyanobacteria clone Z32 from wall biomats in a deep sinkhole in northeastern Mexico, forms a well-supported monophyletic clade, exhibiting 97.51-99.28% nucleotide similarity. These findings suggest that these uncultured cyanobacteria likely belong to the genus Parabrasilonema, broadening our understanding of its diversity across distinct habitats.

Keywords: Cyanobacteria; New genus; Parabrasilonema, Polyphasic approach; Taxonomy; Yongzhuang Reservoir

Received: March 26, 2025; Revised: June 23, 2025; Accepted: October 6, 2025; Prepublished online: March 31, 2026 

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