Expanding species diversity in the monotypic genera Thalassoporum and Tumidithrix (Pseudanabaenales, Cyanobacteriota) with the description of Thalassoporum mexicanum sp. nov. and Tumidithrix helvetica sp. nov.

The taxonomic identity of two well-documented pseudanabaenalean strains, Pseudanabaena sp. PCC 7367^T and Pseudanabaena sp. PCC 7403^T, isolated from the samples collected from the surface of a snail shell in an intertidal zone and sphagnum bog, respectively, was reassessed using a polyphasic approach. The results from the morphological, phylogenetic, ITS rRNA and genomic analyses confirmed that PCC 7367^T (=BACA0810^T) and PCC 7403^T (=BACA0811^T) represent novel species of the monotypic pseudanabaenalean genera Thalassoporum and Tumidithrix, respectively, for which we propose the names Thalassoporum mexicanum sp. nov. and Tumidithrix helvetica sp. nov. in accordance with the International Code of Nomenclature of Prokaryotes. The analysis of the 16S-23S ITS rRNA region, a widely used genetic marker for the delineation of closely related species, effectively distinguished the Thalassoporum species. However, the closely related species within Tumidithrix could not be demarcated using the currently accepted nucleotide dissimilarity cutoff for species delineation but were clearly distinguished through genomic analyses. Accordingly, a revised ITS rRNA nucleotide dissimilarity cutoff is proposed for species delineation within the genus Tumidithrix. Furthermore, genomic investigations revealed that the predicted biosynthetic gene clusters in the genome assemblies of PCC 7367^T and PCC 7403^T were not associated with any known natural products.