Phylogenetic and morphological characterization of Komarekiella atlantica (Cyanobacteria, Nostocales) from southernmost subtropical Brazilian environments.

Terrestrial cyanobacteria occur on diverse substrates (e.g., soil, rock, tree trunks), play a fundamental ecological role by enhancing soil retention, increasing the organic matter and nutrients, and fixing the atmospheric nitrogen, and can produce cyanotoxins. In Brazil, research on these organisms is insufficient given the country’s vast territory and wide range of environments. Hitherto, most studies have focused on the Southeast region, with a small number on the North and Northeast. In Rio Grande do Sul state (South), it seems there are solely seven papers, where only three were based on polyphasic approaches. It was observed that, during the studies on terrestrial cyanobacteria in this state, populations phenotypically similar to Nostoc are highly diversified. Three Nostoc-like strains were isolated from different environments in southernmost subtropical Brazilian Atlantic rainforest (HASC 224) and Pampa (HASC 204 and HASC 229) biomes and studied using morphological and molecular approaches. The Maximum Likelihood and Bayesian Inference phylogenies of 16 S rRNA gene show that these strains are closely related to nostocacean strains and grouped in strongly supported clades within Komarekiella atlantica (99.7% to 100%). Moreover, ITS analyses of the three strains confirmed their affiliation to K. atlantica. Despite their very close genetic relationship, morphological differences among their populations were observed, as well as distinctions in relation to the original description of the species. The reason why such divergence occurs is not conclusive. It could be morphological expressions of the same species or a response to environmental conditions. Therefore, further analyses based on other molecular markers or on the whole genome are necessary to clarify this issue. These pioneering findings in subtropical Brazilian environments of Rio Grande do Sul state expand the knowledge of the morphological variability, phylogeny, geographical distribution, and habitat of K. atlantica, allowing the elaboration of an amended description of this species.