First observation of Trichormus sp. 121B (Nostocales, Nostocaceae) isolated from freshwater in Iran, using a polyphasic approach

In an effort to increase the knowledge of the diversity of cyanobacteria from the Golestan province in Iran, we have isolated a Trichormus- like cyanobacterium. The strain designated as 121B was studied using a polyphasic approach that combined morphological, ecological, and phylogenetic analyses of the 16S-23S internal transcribed spacer (ITS) rRNA gene region. Additionally, phylogenetic relationships were inferred using the p-distance method. A total of 149 sequences were included in this comprehensive phylogenetic analysis to ensure robust evolutionary insights. The results showed that the strain was morphologically indistinguishable from the genus Trichormus, but phylogenetic analyses based on Bayesian Inference and Maximum Likelihood (ML) methods placed the strain in a separated monophyletic and highly supported (96.3% ML) genus-level cluster, distant from Trichormus sensu stricto and with Cyanocohniella as sister taxa. The calculated p-distance for the 16S rRNA gene also reinforced 91% similarity with the other Trichormus species. The D1-D1’ and Box-B secondary structures showed the uniqueness of this strain, as it shared no similar pattern with closest genera within the Nostocales. For all these reasons, and in accordance with the International Code of Nomenclature for Algae, Fungi and Plants, we here described the phylogeny of Trichormus sp. 121B.