Sivoneniella epilithica gen. et sp. nov., (Leptolyngbyaceae, Cyanobacteria), from Suomenlinna Fortress (UNESCO World Heritage Site), Finland

Cyanobacteria are an ancient and diverse group of oxyphototrophic bacteria found across a wide range of environments. The taxonomic diversity of terrestrial cyanobacteria inhabiting rock surfaces remains poorly studied despite their key role as pioneering species in ecological succession. We isolated two phycoerythrin-rich strains resembling the genus Leptolyngbya in a survey of filamentous cyanobacteria from previously unstudied epilithic habitats on the Suomenlinna Fortress (UNESCO World Heritage site) in Finland. We employed a comprehensive polyphasic approach to characterize these isolates to account for the known polyphyletic nature of Leptolyngbya and the presence of cryptic taxa. Our analyses revealed that the two strains form a distinct and well-supported clade within the family Leptolyngbyaceae. Therefore, we propose a new monospecific genus, Sivoneniella, following the International Code of Nomenclature for Algae, Fungi, and Plants. Secondary structures of conserved 16S–23S ITS regions (D1–D1’, box B and V3 helices), ITS per cent dissimilarity, multi-locus phylogenies (16S rRNA, rbcLX, rpoC1), and genome-based phylogenomic analyses all support the recognition of this novel cryptic genus. Genome mining and LC-MS analyses revealed the absence of known cyanotoxins in both strains (UHCC 1019T and UHCC 1020), and their cell extracts exhibited no inhibitory effects on the growth of relevant pathogenic bacteria and fungi. These findings advance our understanding of cyanobacterial diversity in terrestrial ecosystems, support the establishment of Sivoneniella as a new genus within the order Leptolyngbyales and explore the biotechnological potential of phycoerythrin-rich strains of S. epilithica. We describe a new cryptic genus of epilithic, phycoerythrin-rich cyanobacteria, Sivoneniella.Sivoneniella is the first genus of cyanobacteria described from an UNESCO monument in Finland.The proposed unification of Plectolyngbya and Radiculonema with Leptolyngbya warrants re-evaluation. We describe a new cryptic genus of epilithic, phycoerythrin-rich cyanobacteria, Sivoneniella. Sivoneniella is the first genus of cyanobacteria described from an UNESCO monument in Finland. The proposed unification of Plectolyngbya and Radiculonema with Leptolyngbya warrants re-evaluation.