An isolated lichenicolous fungus forms lichenoid structures when co-cultured with various coccoid algae.

We present experimental data on a lichen-inhabiting fungus which forms sterile dark coloured mycelia on thallus areoles of Lecanora rupicola.The lichenicolous fungus, tentatively named ALr-1, grows readily in solid media and is able to develop lichenoid structures when co-cultured with various coccal algal species in vitro.After an initial formation of phototropic hyphal bundles through initially free-living algal colonies, the lichenoid structures develop as a fungal surface layer, an algal rich layer, and lower layer formed exclusively by hyphae.Scanning electron micrographs show close contacts between the fungus and the algae by formation of appressoria.Re-inoculation of the host species resulted in a more detrimental interaction, in which a dense brown mycelium extends through the upper layers of the lichen.This phenotype has not yet been observed in nature and likely results from the particular experimental conditions.The fungus is not closely related to any other known parasitic species known on the native host species.A phylogenetic hypothesis of LSU and SSU rDNA indicates a relationship of ALr-1 basal to Chaetothyriomycetidae.The Iichenoid structure of ALr-1 establishes more rapidly in vitro than re-synthesised lichen bionts and could represent an interesting model to study mutualistic interactions between fungi and algae.