Systematics and biogeography of sciophilous cyanobacteria; an ecological and molecular description of Albertania skiophila (Leptolyngbyaceae) gen. & sp. nov.

Filamentous cyanobacteria grow as phototrophic biofilms in Maltese hypogea. Within these sheltered habitats, the prevailing relative humidity is high throughout the year, water seeps through the porous calcareous substrata and the irradiance is minimal. Isolated sciophilous cyanobacterial strains, adapted to tolerate and thrive in such environments, were studied using cytomorphological, ecological and genetic approaches. Light and electron microscopy revealed simple green trichomes 2-3 mu m wide, made up of cells with parietal thylakoids, a rounded apical tip and surrounded by multistratified colourless sheaths. Phylogenetic analysis based on the 16S ribosomal RNA gene resulted in a new cluster of sequences that indicated a separate position at the generic level and justified the creation of the new genus Albertania. The strains were closely related (98% similarity or higher) and distantly related to other established cyanobacterial taxa (< 95%). The 16-23S internal transcribed spacer secondary folding structures were also unique. The clade consisted of six sequences isolated from phototrophic biofilms growing in five hypogea in Malta and Italy that are geographically isolated. The strains are described as Albertania skiophila gen. & sp. nov. since they form a monophyletic cluster made up of strains having a similar cytomorphology, ecology and molecular biology from two disjunct regions in Europe. Albertania skiophila strains are endemic to a specific habitat and distinct geographical region, leading to a defined biogeographical distribution in hypogea and caves around the Mediterranean region.