Amazoninema gen. nov., (Synechococcales, Pseudanabaenaceae) a novel cyanobacteria genus from Brazilian Amazonian rivers.

The genus Leptolyngbya includes morphotypes with thin cells and simple morphology, and is one of the most common cyanobacterial genera found in a wide range of environments. In many cases, however, the morphotypes assigned to this genus do not share a common ancestor based on 16S rRNA gene phylogeny, which has led to the description of novel genera, such as Nodosilinea, Oculatella, Pantanalinema, Alkalinema, Thermoleptolyngbya, Onodrimia, Timaviella and Toxifilum. Thus, four novel isolates, with a comparable morphology to Leptolyngbya, were recovered from the Amazon and Solimões rivers. The novel 16S rRNA gene sequences obtained from these strains were placed together as a new and distinct phylogenetic lineage that is more closely related to the clusters embracing the genera Nodosilinea, Haloleptolyngbya and Halomicronema than to the genus Leptolyngbya. Additionally, these novel 16S rRNA gene sequences showed similarity values lower than 95 % compared with those from the most phylogenetic related groups and/or established genera. Altogether, these results supported the erection of a novel genus, named Amazoninema, to accommodate the novel isolates. Likewise, a comparison of their 16S rRNA gene sequences revealed similarities higher than 99.8 %, indicating that they belong to a single species, which was corroborated by analysing their 16S-23S internal transcribed spacer regions and unique Box-B helix pattern. Few studies have been undertaken to uncover the cultured diversity of cyanobacteria from Amazonia, and to our knowledge, this is the first cyanobacteria genus erected, considering morphotypes isolated exclusively from Brazilian Amazonian rivers.