Abstract
Since 1965 a cyanobacterial strain termed ‘Fischerella ambigua 108b’ was the object of several studies investigating its potential as a resource for new bioactive compounds in several European institutes. Over decades these investigations uncovered several unique small molecules and their respective biosynthetic pathways, including the polychlorinated triphenyls of the ambigol family and the tjipanazoles. However, the true taxonomic character of the producing strain remained concealed until now. Applying a polyphasic approach considering the phylogenetic position based on the 16S rRNA and the protein coding gene rbcLX, secondary structures and morphological features, we present the strain ‘Fischerella ambigua 108b’ as Symphyonema bifilamentata sp. nov. 97.28. Although there is the type species (holotype) S. sinense C.-C. Jao 1944 there is no authentic living strain or material for genetic analyses for the genus Symphyonema available. Thus we suggest and provide an epitypification of S. bifilamentata sp. nov. 97.28 as a valid reference for the genus Symphyonema. Its affiliation to the family Symphyonemataceae sheds not only new light on this rare taxon but also on the classes of bioactive metabolites of these heterocytous and true-branching cyanobacteria which we report here. We show conclusively that the literature on the isolation of bioactive products from this organism provides further support for a clear distinction between the secondary metabolism of Symphyonema bifilamentata sp. nov. 97.28 compared to related and other taxa, pointing to the assignment of this organism into a separate genus.
Highlights
True-branching heterocytous cyanobacteria were formerly classified as Stigonematales [1], but various phylogenetic analyses have shown that the Nostocales form a monophyletic lineage within which the true-branching genera are scattered in several unrelated families, making Stigonematales polyphyletic [2,3] and an outdated taxon distinction
As there is no culture material or genetic information of any other Symphyonema species available, we suggest that S. bifilamentata sp. nov. should act as reference point for the genus along with an epitypification and emendation of the genus Symphyonema provided here
The strain originally termed Fischerella ambigua 108b/ CCAP1427/4/ 97.28 was found to be unique based on its ecology, morphology, distribution, phylogeny and secondary structures of the 16S-23S ITS gene region and not related to Fischerella ambigua
Summary
True-branching heterocytous cyanobacteria were formerly classified as Stigonematales [1], but various phylogenetic analyses have shown that the Nostocales form a monophyletic lineage within which the true-branching genera are scattered in several unrelated families, making Stigonematales polyphyletic [2,3] and an outdated taxon distinction.True-branching Nostocalean genera have the most complex morphological traits across the whole phylum Cyanobacteria, including various cell types, branching patterns, and thalli structures. This wealth of striking morphological differences and characteristics that one might set into phylogenetic relations exists, it has been shown that true-branching cyanobacteria are polyphyletic based on genetics [2], and more recently based on heterocyte glycolipids [4]. According to the current taxonomic classification of cyanobacteria established by Komárek et al in 2014 [3], the true-branched taxa are placed in the five families Symphyonemataceae (13 genera), Hapalosiphonaceae (28 genera), Stigonemataceae (5 genera), Capsosiraceae (4 genera) and Chlorogloeopsidaceae (1 genus) This makes a total of 51 genera of which only 11 (Westiella, Spelaeonaias, Iphinoe, Loriellopsis, Chlorogloeopsis, Aetokthonos, Mastigocladus, Mastigocoleus, Westiellopsis, Neowestiellopsis, Reptodigitus) are supported by molecular data such as the 16S rRNA and only a few of them comprising the holotype species
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