Phytotaxa

In this study, novel Calothrix-like strains NUACC09 and NUACC10 were isolated from the surfaces of rocks in Phayao Lake, Thailand. Morphological, molecular and ecological comparisons were investigated to characterize the taxonomic status of these novel strains. Under the light microscope, morphological studies indicated that these two strains were morphologically similar to Calothrix but could be differentiated by production of a non-hyaline hair at the terminal end, a low degree of tapering, twisted or loop-forming filaments, a knotted growth form, intertwined trichomes and presenting more than one trichome within the single sheath. In the 16S rRNA and rbcLX gene phylogenetic tree analyses, our strains formed a monophyletic clade with former freshwater/terrestrial Calothrix-like taxa separating distantly from other Calothrix-like genera. Furthermore, low 16S rRNA gene sequence similarity (<94.9%) to the closely related genera and species delimitation analyses (PTP/bPTP, GMYC, ABGD and ASAP methods) indicated that this clade should be considered as a different cyanobacterial lineage. The phylogenetic tree and secondary structures (D1–D1′, V2, Box-B and V3 helix) based on 16S–23S rRNA ITS regions suggested that multiple species might be contained in this clade. Therefore, here, Phayaothrix was proposed as a novel cyanobacterial genus with Phayaothrix lacustris sp. nov. as the type species following the International Code of Nomenclature for algae, fungi and plants.

Very thin filamentous cyanobacteria are ubiquitous in a wide range of environments. For many years they were traditionally studied according to their morphological properties only. With the introduction of additional taxonomic methods (cytomorphological analyses, molecular sequencing, exact ecological studies, better data about phytogeographical distribution), traditional genera such as Leptolyngbya and Phormidium were found to be polyphyletic. Phormidesmis belonged to a newly formed genus that was supposed to explain the variability of such very thin simple filamentous cyanobacteria. However, even after definition of Phormidesmis based on distinct cytomorphological and phylogenetic traits, the variability within this genus remained unresolved. Here we analyzed 26 Phormidesmis strains to describe the variability within this genus, classified two new species (P. arctica and P. communis) and transferred Leptolyngbya nigrescens into P. nigrescens. A tabular review of Phormidesmis species is included. The diacritical features of all these species are: width up to 1–4 µm, barrel-shaped cells, which can be shorter or slightly longer than wide, with apparent constrictions at the cross-walls. Our study shows that Phormidesmis is a morphologically and genetically well-defined genus with a global distribution. A newly described genus Leptodesmis has significant morphological similarities both with Phormidesmis and Leptolyngbya, however with intermediate phylogenetic position with significant divergence in 16S rRNA gene. Leptodesmis is cryptic both to Phormidesmis and Leptolyngbya. In the initial part of the life cycle resembles Leptolyngbya, the appearance of older trichomes change to Phormidesmis like morphology.

A total of 48 strains of thin, filamentous cyanobacteria in Synechococcales were studied by sequencing 16S rRNA and rpoC1 sequence fragments. We also carefully characterized a subset of these by morphology. Phylogenetic analysis of the 16S rRNA gene data using Bayesian inference of a large Synechococcales alignment (345 OTU’s) was in agreement with the phylogeny based on the rpoC1 gene for 59 OTU’s. Both indicated that the large family-level grouping formerly classified as the Leptolyngbyaceae could be further divided into four family-level clades. Two of these family-level clades have been recognized previously as Leptolyngbyaceae and Prochlorotrichaceae. Oculatellaceae fam. nov. and Trichocoleaceae fam. nov. are proposed for the other two families. The Oculatellaceae was studied in greater detail, and six new genera containing 14 species were characterized and named. These new taxa are: Pegethrix botrychoides, P. olivacea, P. convoluta, P. indistincta, Drouetiella lurida, D. hepatica, D. fasciculata, Cartusia fontana, Tildeniella torsiva, T. nuda, Komarkovaea angustata, Kaiparowitsia implicata, Timaviella obliquedivisa, and T. radians.