The subaerophytic cyanobacterium Oculatella subterranea (Oscillatoriales, Cyanophyceae) gen. et sp. nov. : a cytomorphological and molecular description

Abstract

A new genus and species of subaerophytic cyanobacteria with very thin purple-red trichomes are described. The seven strains included in this genus were isolated from phototrophic biofilms growing on calcareous substrata in ancient hypogea. Trichomes were 1-3 μm thick, with small constrictions at the cross-walls and colourless sheaths. The thylakoid arrangement was parietal. Autapomorphic characters include the purple-red colouration of cells and a photosensitive orange spot at the tip of the trichome containing a rhodopsin-like pigment. Molecular and phylogenetic analyses based on 16 S rRNA gene sequences, resulted in a new 16 S rRNA cluster that indicated a separate position at the generic level. All strains were closely related (99% or higher similarity) and distantly related to other established cyanobacterial taxa (92%). The 16 S-23 S rRNA internal transcribed spacer (ITS) sequence of five of the red strains was almost identical. The ITS secondary folding structure was also unique to these strains and different to the Leptolyngbya type species. These strains have only been isolated from subterranean environments so far, and considering also this unique biotope and their particular ecology, we propose the new genus and species Oculatella subterranea. The genus name Oculatella means 'provided with a small eye'. The new genus is described using combined molecular and cytomorphological criteria, in accordance with the nomenclatorial recommendations of both the Bacteriological Code and the Botanical Code of Nomenclature. The genus Oculatella is of common distribution in hypogea and has been isolated from all hypogean environments so far studied in Rome and Malta. The type strain is VRUC135.