Polyphyly of true branching cyanobacteria (Stigonematales)

Abstract

Cyanobacteria with true branching are classified in Subsection V (formerly order Stigonematales) in the phylum Cyanobacteria. They exhibit a high degree of morphological complexity and are known from particular biotopes. Only a few stigonematalean morphotypes have been cultured, and therefore the high variability of morphotypes found in nature is under-represented in culture. Axenic cultures of Chlorogloeopsis and Fischerella sensu Rippka et al. were, to date, the only representatives of this Subsection in phylogenetic studies. The 16S rDNA sequence analysis data in this report confirm that heterocyst-forming cyanobacteria are a monophyletic group. However, unlike previous studies have suggested, these 16S rDNA data on new Stigonematales strains show that the true branching cyanobacteria are polyphyletic and can be separated into at least two major groups defined by their branching type, the first group being characterized by T-branching and the second group by Y-branching. Cyanobacteria with intercalary heterocysts and either no branching or false-branching also formed separate clusters. In consequence, our phylogenetic data do not correlate with the bacteriological and traditional classifications, which distinguish filamentous heterocystous cyanobacteria with or without true branching (Nostocales/Stigonematales).

Phylogenetic analysis of heterocystous cyanobacteria (Subsections IV and V) using highly iterated palindromes as molecular markers

“…On shifting to the branched heterocystous clade, the genera under study were Hapalosiphon, Westiellopsis, Fischerella, Nostochopsis, and Mastigocladus. All the strains that were represented by the true branching heterocystous cyanobacteria showed ample proof of the polyphyletic origin of the order Stigonematales along with confirming to the well-postulated intermixing tendencies amongst the subsections IV and V of the heterocystous clade of cyanobacteria (Gugger and Hoffmann 2004;Mishra et al 2013;Singh et al 2013). In other words, it is also evident that the branched heterocystous cyanobacteria show very similar phylogenetic affinities with their unbranched heterocystous counterparts, suggesting that the entire heterocystous clade is monophyletic in origin whereas the stigonematalean heterocystous cyanobacteria are polyphyletic in origin.…”

“…PCA analysis placed the Calothrix strains at different levels and clusters with its affinities being evident with unbranched, false branched, and even true branched strains. The false branching genera that were studied comprised of Scytonema and Tolypothrix, and their phylogenetic affiliations were also very much like the other unbranched heterocystous cyanobacteria with all the strains showing no clear cut clustering patterns, neither in the phylogenetic trees nor the PCA clusters, that could be in coherence with the traditional scheme of cyanobacterial taxonomy (Gugger and Hoffmann 2004;Palinska et al 1996). Finally, the only representative of its genera Anabaenopsis sp.…”

Spatio-temporal variability in Mediterranean rocky shore microphytobenthos

“…6). It should be noted that the genus Rivularia, which belongs to the family Rivulariaceae, is classified according to the National Center for Biotechnology Information taxonomy and the revision of the order Stigonematales within the order Nostocales (also see Gugger & Hoffmann 2004). Among heterotrophic bacteria, Bacteroidetes was the most abundant group.…”

PCR based fingerprinting of Westiellopsis cultures with short tandemly repeated repetitive (STRR) and highly iterated palindrome (HIP) sequences

“…Members of this subsection exhibit high degree of morphological complexity and the high variability of the morphotyopes in nature is usually under-represented in culture (Gugger & Hoffman 2004). The habitats of the genus Westiellopsis include freshwater and sub-aerial biotopes such as acidic oligotrophic lakes or caves.…”