Towards a phylogenetic position for the morphologically-defined genus Pannus (Cyanobacteria)
da Silva Malone, Camila Francieli; Alvarenga, Danillo Oliveira; Fiore, Marli Fátima; Sant'Anna, Célia Leite
The morphologically-defined genus Pannus containing members of unicellular cyano-bacteria, has been variously classified belonging to the families Microcystaceae, Merismopediaceae, and Synechococcaceae. The phylogeny of Pannus, which possesses cells disposed in one layer at the mucilage surface, two planes of cell division and no gas vesicles, has yet to be developed. In this study, in a combined approach of morphological and ultrastructural analyses, 16S rRNA phylogeny and comparison of the ITS nucleotide sequence and secondary structure, the status of a Pannus strain isolated from a Brazilian wetland area was examined. Morphologically, the new strain CCIBt3594 showed all the diagnostic traits of the genus Pannus according to the original concept. Phylogenetic analysis of 16S rDNA sequence indicated that strain CCIBt3594 is affiliated to the genus Microcystis, but with low similarity (< 94.4%), confirming that this strain indeed belongs to a distinct genus. The evaluation of 16S-23S ITS nucleotide sequence and secondary structure, as well as the disposition of the thylakoid structures, also indicated that strain CCIBt3594 resembles Microcystis. Therefore, the molecular and ultrastructural data obtained in this study corroborate with the initial findings that the genus Pannus belongs to the order Chroococcales and most likely to the family Microcystaceae. This Brazilian strain differs from the already known Pannus species by a larger cell size, absence of individual mucilage and its habitat, and is here described for the first time as Pannus brasiliensis sp. nov.