Taxonomic insights into [i]Nostoc[/i]: Integrating a polyphasic approach for the identification of novel species and a new genus from polar and temperate ecosystems

Abstract

The genus Nostoc is a ubiquitous and morphologically complex group of cyanobacteria that thrive in a remarkable diversity of freshwater, terrestrial, and extreme environments. However, its taxonomy remains problematic and heterogeneous owing to its historical reliance on morphological characteristics, resulting in over 300 described species and a polyphyletic genus structure, necessitating modern molecular evaluation. To address these challenges, this study applied a polyphasic approach to classify thirteen cyanobacterial strains from the BCCM/ULC collection at the University of Liège. The methodology included morphological characterization via light microscopy, PCR amplification and sequencing of the 16S rRNA gene and the 16S–23S ITS region, phylogenetic analyses, evaluation of 16S rRNA sequence similarity, and assessment of ITS sequence dissimilarity along with secondary structures of conserved regions (D1-D1', Box-B, V3 helices). The results indicated significant cryptic diversity, with several strains likely representing novel species within the Nostoc sensu stricto clade and a novel genus closely related to Nostoc. This study highlights the necessity of the polyphasic approach in cyanobacterial taxonomy and pinpoints the ongoing challenges in cyanobacterial systematics