Axenic culture and biosynthesis of secondary compounds in lichen symbiotic fungi, the Parmeliaceae

Abstract

Lichens produce unique secondary metabolites with a rich potential as bioactive compounds. In many cases, the use of these molecules is limited by the low concentration of these compounds in thalli, low growth rate in culture, and changes in chemical patterns between thalli and aposymbiotic culture. In addition, the massive collection of some species of industrial interest can cause damage to lichen diversity and the associated environment. Six lichenized fungi (Arctoparmelia centrifuga, Parmelia saxatilis, Parmelina tiliacea, Platismatia glauca, Xanthoparmelia tinctina, and Usnea ghattensis) with biotechnological interest and belonging to Parmeliaceae have been cultured in order to test culture conditions and obtain enough biomass for further studies. In addition, we analyzed the compounds synthetized in axenic conditions and they were compared with chemosyndromes identified in complete thalli. Arctoparmelia centrifuga, P. saxatilis, P. tiliacea and X. tinctina were successfully cultivated while for P. glauca and U. ghattensis we only obtained sporulation and germination of the spores. The chemical pattern of the compounds secreted into the culture media varied significantly from the chemosyndrome of the whole thallus. Phenolic compounds of pharmacological and industrial interest (usnic acid, aspicilin, α-alectoronic acid, physodic acid, lobaric acid and nordivaricatic acid) and a wide variety of potentially bioactive compounds were obtained during the culture process.

Lichen Depsidones with Biological Interest

“…The interactions between the mycobiont and photobiont affect the production of secondary metabolites in lichens. For example, several studies have shown that mycobionts within the lichen thallus produce a variety of secondary metabolites in contrast with axenic mycobiont cultures 22 , 23 , 24 . The production of secondary metabolites in the lichen thallus has also been found to be affected by environmental factors (i.e., UV-radiation, climatic conditions, habitats, and presence of non-photosynthetic bacteria and other fungi in lichen thallus) 25 , 26 , 27 , 28 , 29 , 30 .…”

Lichen cell factories: methods for the isolation of photobiont and mycobiont partners for defined pure and co-cultivation

“…There are some successful isolations described for lichen fungi from different groups, e. g. foliose, crustose and fruticose lichens [e.g. 23 – 25 ]. The success of different methods for a specific species, however, was not compared yet.…”