Description of <i>Flavicapitulum</i> gen. nov. and two new species of <i>Marmoreocelis</i> from thermal habitats in the Americas

Abstract Three novel taxa in the Coleofasciculales were observed in hot springs in Yellowstone National Park, Wyoming, United States, and in the Tabaconcito thermal springs on the Rio Tabacón in Costa Rica. Flavicapitulum vaporiphilum gen. et sp. nov. was located in a supported clade with Gracilinea and Marmoreocelis. It is genetically distant from Marmoreocelis , but genetic separation from Gracilinea is ambiguous based on percent identity of the 16S rRNA gene. However, Flavicapitulum forms a phylogenetically supported monophyletic clade and is ecologically distinct from both other genera by inhabiting fumaroles. It is further distinguished by the possession of yellowish apices in mature trichomes. Marmoreocelis minervensis sp. nov. is distinguished from the type species by habitat preference (hot springs vs. biological soil crusts) and phylogeny and belongs to a large clade containing many other uncultured hot spring Cyanobacteria. Marmoreocelis tabaconcitensis sp. nov. was represented by a single strain isolated from a hot spring in Costa Rica. This study demonstrated that the resolution of the two families in the Coleofasciculales is unclear. Placement based on genomic phylogenies in the last major revision of cyanobacterial taxonomy is not in agreement with the phylogeny based on the 16S rRNA gene of this study. A synapomorphy defining the supported clade containing Wilmottia is the presence of only a single tRNA gene, tRNA Ile , in the 16S–23S ITS rRNA region. Coleofasciculus contains two tRNA genes in its ITS rRNA region, tRNA Ile and tRNA Ala . This difference in ITS rRNA regions as well as the 16S rRNA gene phylogeny support tentative placement of Flavicapitulum, Gracilinea , and Marmoreocelis in Wilmottiaceae at present.