Plectolyngbya hodgsonii: a novel filamentous cyanobacterium from Antarctic lakes

A special cluster of filamentous, false-branched cyanobacteria, isolated from littoral mat samples in coastal lakes of the Larsemann Hills region (coll. by D. Hodgson) was studied by a polyphasic approach. This morphotype has several characters corresponding to the traditional genera Leptolyngbya (morphology of trichomes), Pseudophormidium (type of false branching) or Schizothrix (occasional multiple arrangement of trichomes in the sheaths). However, this cluster of strains is distinctly isolated according to its phylogenetic position (based on 16S rRNA gene sequences), and thus, a separate generic classification is justified. The cytomorphology of this generic entity is also characteristic. Therefore, a new genus (Plectolyngbya with the type species P. hodgsonii) was described. The same cyanobacterial morphotype was found in the littoral zone of the partially frozen inland Monolith Lake in the northern, deglaciated area of James Ross Island, in the NW part of the Weddell Sea. Plectolyngbya hodgsonii occurs evidently in more Antarctic lakes of the continental type, under very particular conditions (littoral with average temperature below 3°C during the Antarctic summer season, with periodical drying and freezing for more than 8 months in a year). The valid definition, phenotype documentation and ultrastructural characters of this cyanobacterium are presented in this article. Morphologically (and possibly genetically) similar types are common in other habitats in various regions and represent probably different species.