Siamcapillus rubidus gen. et sp. nov. (Oculatellaceae), a novel filamentous cyanobacterium from Thailand based on molecular and morphological analyses

Abstract

Cyanobacterial diversity has been extensively studied; however, scant knowledge exists concerning genetic data and higher accuracy for tropical cyanobacterial diversity. In particular, the existence of unnamed monophyletic genera within the Oculatellaceae requires further investigation. Here, two novel strains (NUACC13 and NUACC14) were isolated from a cyanobacterial mat covering border soil of a small freshwater pond in Phitsanulok Province, Thailand. A polyphasic approach combining genetic (16S rDNA and rpoC1 gene phylogenies, evolutionary distance and ITS secondary structures) and morphological information was applied to evaluate the taxonomic status of these novel strains. All phylogenetic analyses of 16S rDNA and rpoC1 gene sequences placed our strains within the Oculatellaceae, strongly supporting a novel monophyletic clade that did not belong to other known Oculatellaceae genera. The 16S rDNA sequence similarity  (<96.2%) values among the closest described genera also supported the novelty of our strains. The hypothetical secondary structures (D1–D1′, Box-B, V2 and V3 helices) of the ITS region confirmed the uniqueness of our strains, indicating differences from the related genera. Morphological features of the novel strains differed from the phylogenetically closest taxa by size and color of filament and vegetative cell and the presence of a frayed sheath. Considering all the results, we herein described our strains as the novel genus Siamcapillus gen. nov. in the Oculatellaceae with the type species S. rubidus sp. nov.