Description of the cyanobacterial genus Desmonostoc gen. nov. including D. muscorum comb. nov. as a distinct, phylogenetically coherent taxon related to the genus Nostoc.

Abstract

On the basis of data presented here and in earlier studies, Desmonostoc gen. nov. is described. The new genus includes the traditional species Nostoc muscorum agardH ex Bornet et FLaHauLt 1888, and several other strains previously assigned to the genus Nostoc, which present similar morphology and phylogenetic placement within the Desmonostoc lineage. The Desmonostoc clade is phylogenetically coherent according to 16S rRNA gene sequence analysis performed with four distinct approaches. In all phylogenetic trees, Desmonostoc formed a supported group separated from strains belonging to the related taxa Nostoc, Trichormus, and Mojavia. We also suggest that other clusters hosting strains which for their morphology resemble Nostoc, but are more distant from Nostoc commune cluster than Desmonostoc, should be reclassified into new genera in the future. Strains belonging to Desmonostoc form long vegetative filaments embedded in diffluent mucilaginous envelopes, except for primordial stages they never form a firm periderm, and the filaments are never densely coiled with compact trichomes as found in Nostoc. Both terminal and intercalary heterocytes occur, and mostly elliptical akinetes were differentiated apoheterocytically in long chains. Desmonostoc strains can be usually found in moist or wet meadow, field and forest soils, more rarely in periphyton, but to our knowledge, they are missing or very rare in desert areas. Some of these strains have been found to grow in association with mosses or as symbionts of cycadean plants and of Gunnera sp.

Two new species of Phyllonema (Rivulariaceae, Cyanobacteria) with an emendation of the genus

“…These morphologically divergent species are placed in this genus based on the weight of molecular sequence analysis alone. This is contrary to the present trend in cyanobacterial and algal taxonomy in which taxa with minor morphological differences have been placed in separate genera based upon phylogenetic evidence( Reh akov a et al 2007, Siegesmund et al 2008, Turicchia et al 2009, Struneck y et al 2011, Hrouzek et al 2013, Bohunick a et al 2015b, and many Synechococcales-see Kom arekand Johansen 2015, Kom arek et al 2014.FIG. 5.…”

“…In most taxonomic papers, one of two outcomes has occurred when both molecular and morphological evidence has been considered. First and most commonly, molecular data and morphological data are congruent, and seemingly minor morphological or ecological differences in populations/cultures are reinforced by the molecular data, leading to the description of new species or genera (Flechtner et al 2002, Reh akov a et al 2007, Turicchia et al 2009, Struneck y et al 2011, Hrouzek et al 2013. Second, very similar phenotypes can be found to be phylogenetically diverse, resulting in the creation of cryptic or pseudocryptic taxa , Osorio-Santos et al 2014, Miscoe et al 2016, Shalygin et al 2017.…”

Komarekiella atlantica gen. et sp. nov. (Nostocaceae, Cyanobacteria): a new subaerial taxon from the Atlantic Rainforest and Kauai, Hawaii

“…Phylogenetic studies based on 16S rRNA gene sequence have shown that strains assigned to Nostoc do not form a monophyletic group (Hrouzek et al 2005;Řeháková et al 2007;kaštovský & JoHansen 2008;Lukešová et al 2009;JoHansen et al 2014), and recently three new Nostoclike genera, phylogenetically closely related to Nostoc sensu strictu, have been described: Mojavia Řeháková et JoHansen in Řeháková et al (2007), Desmonostoc Hrouzek et ventura in Hrouzek et al (2013), and Halotia genuário et al (2015). Despite this progress, further revisionary work of the Nostocaceae is expected as new strains are isolated and characterized using both molecular and morphological characters.…”

A detailed morphological, phylogenetic and ecophysiological analysis of four benthic Anabaena (Nostocales, Cyanobacteria) strains confirms deep heterogeneity within the genus

“…in this cluster, and further polyphasic examinations will be required before any decision can be made. Strains of other species assigned to Trichormus (T. azollae and T. doliolum) clustered in completely different positions in the tree, once again emphasizing the polyphyly of the genus (rajanieMi et al 2005;HrOuzeK et al 2013), which is in urgent need of a comprehensive taxonomic revision.…”