The extremophile Eurychoronema bolivianum gen. et sp. nov. (Nodosilineales, Cyanobacteria) and Leptolyngbya aquatica comb. nov

Extreme environments exhibit conditions that are beyond the tolerances of most species. They are characterized by extremes in temperature, pressure, gas concentrations, salinity, radiation, pH or water availability. Despite their harsh conditions, extreme environments are a rich source for discovering new cyanobacterial taxa. The Bolivian Altiplano is an extreme environment characterized by sub-freezing temperatures, high salinity and some of the lowest precipitation rates on Earth. From this environment, the homocytous filamentous strain LEGE 231228 was isolated. Our 16S rRNA gene phylogenetic analyses showed that this strain was positioned within a clade, sister to a cluster containing Toxifilum and Sodaleptolyngbya strains, in the Nodosilineales clade. The 16S rRNA gene identity analysis revealed that when comparing LEGE 231228 with Toxifilum and Sodaleptolyngbya, the maximum values reached only 94.3% and 93.6%, respectively. Morphologically, LEGE 231228 differed from Sodaleptolyngbya and Toxifilum primarily by forming fascicles and having sheaths that sometimes envelop more than one trichome. Based on these findings, we propose Eurychoronema bolivianum gen. & sp. nov. Additionally, the 16S rRNA gene phylogenies and identity, alongside morphological and 16S-23S ITS analyses permitted us to transfer the Leptolyngbyaceae genus Radiculonema into Leptolyngbya. Radiculonema was nested within the Leptolyngbya clade and both genera shared 95.1% 16S rRNA identity. There was also no morphological difference between these two genera. We also demonstrate that conclusions based on secondary structures of the 16S-23S ITS region alone can be interpreted in different ways.