New insights into Chroococcus (Cyanobacteria) and two related genera: Cryptococcum gen. nov. and Inacoccus gen. nov.

Many cyanobacterial morphospecies with hemispherical cells have been assigned to the genus Chroococcus, but increasingly genetic information has shown that the genus is polyphyletic. Here we describe two new genera based on two new species, Inacoccus gen. nov. based on Inacoccus carmineus sp. nov. and Cryptococcum gen. nov. based on Cryptococcum brasiliense sp. nov. Both genera have morphological features typical of the genus Chroococcus and are based on strains isolated from terrestrial habitats of the Brazilian Atlantic Forest. Inacoccus differs from Chroococcus in forming nanocytes and by producing an intensely red-coloured sheath. Cryptococcum is a cryptic genus and two species, C. brasiliense and C. komarkovaum, have been recognized by a molecular approach (16 rRNA and 16S-23S ITS sequences). The 16S rRNA gene sequence phylogeny indicates that these proposed genera form monophyletic clades apart from the Chroococcus sensu stricto cluster. Additionally, the tropical species Chroococcus subviolaceus was studied by molecular methods for the first time. The results confirmed a vast phylogenetic diversity hidden under the simple morphology of Chroococcus morphotypes, and show that terrestrial environments are a promising field of research.