Polyphasic description of Ciimarium marinum gen. et sp. nov. (Prochlorococcaceae, Synechococcales): a new picocyanobacterial taxon from the Portuguese coastal ecosystem

In this paper, we describe Ciimarium marinum gen. et sp. nov. (Prochlorococcaceae, Synechococcales) based on 16S rRNA gene phylogenies, 16S-23S ITS secondary structures, ultrastructure (TEM), morphological, pigments and ecological data of “Synechococcus” sp. LEGE 11466. The strain was isolated from a sample collected at Leixões Harbour, Portugal (41°11’08.1”N 8°43’08.8”W) on September 26th, 2011, by scraping an epilithic biofilm under 10-13m depth, less than 1km offshore. Bayesian Inference and Maximum Likelihood phylogenies demonstrate that the Ciimarium sequence is placed in a monophyletic clade with strong phylogenetic support (BI=1, ML=100), within the Prochlorococcaceae cluster. The type strain LEGE 11466 is phylogenetically distant from other reference strains of Cyanobacteria and is grouped with Uncultured “Synechococcus” MLS1228cl3 , “Synechococcus” MLCB, “Cyanobium” ATX 6A2 ATX-6A2-C45 and “Synechococcus” MBIC10613.. The secondary structures of 16S-23S ITS corroborate with the separation of Ciimarium from all the Prochlorococcaceae genera. Also, they show that MLCB and ATX 6A2 ATX-6A2-C45 may be different species from the type LEGE 11466. The ultrastructure analysis shows parietal thylakoids, in agreement with the family description. Morphologically the genus is indistinguishable from other Prochlorococcaceae genera. The pigments analysis shows Zeaxanthin and β-carotene as the main pigments, and also a low concentration of phycocyanin. Finally, our phylogenies indicate that a revision of the Prochlorococcaceae family is necessary, as there are still many Synechococcus-like Cyanobacteria strains that should be described as new genera in the future.