Morphological and Molecular Evaluation of Pseudanabaena epilithica sp. nov. and P. suomiensis sp. nov. (Pseudanabaenaceae, Cyanobacteria) from Finland

Abstract

Cyanobacteria represent a cosmopolitan group of oxyphototrophic bacteria. Although free-living cyanobacteria thriving in aquatic habitats as well as cyanobacteria in terrestrial symbiotic systems (lichens) have been extensively studied in Finland, the diversity of terrestrial rock-inhabiting cyanobacteria is overlooked. As part of an ongoing effort to study terrestrial epilithic cyanobacteria from Finland, we isolated two Pseudanabaena-like cyanobacterial strains and characterized them using a polyphasic approach. Although the two strains were firmly placed within the Pseudanabaena clade in the 16S rRNA phylogenetic analyses, relationships among species were better resolved when phylogenetic analyses were based on a concatenate alignment of 16S rRNA gene and 16S–23S Internal Transcribed Spacer (ITS) region. In addition, 16S–23S ITS percent dissimilarity proved to be more useful for species discrimination in Pseudanabaena compared to secondary structures of conserved 16S–23S ITS domains (D1–D1′, box B, V2 and V3 helices). Considering morphological, molecular and ecological information, we describe P. epilithica sp. nov. and P. suomiensis sp. nov. under the provisions of the International Code of Nomenclature for Algae, Fungi and Plants. Neither toxins nor antimicrobial metabolites were detected during LC-MS analysis or antimicrobial susceptibility testing, respectively. Lastly, our phylogenetic analyses revealed that many Pseudanabaena strains are misidentified and highlight the need for taxonomic revision in this poorly studied cyanobacterial genus.