Advanced methods for the study of the chemistry and the metabolism of lichens

Lichens are compound entities of a fungal partner (“mycobiont”) and one or more photosynthetically active algae or cyanobacteria (“photobionts”). The organisms live in an intimate, symbiotic association which has been classified as a mutualistic or controlled parasitic relationship. Several metabolites from lichens display unique structures with unknown functions, and only a few model species have been analysed comprehensively. The complex metabolic interplay between the organisms in lichens is also incompletely understood. Earlier experiments with ¹⁴C-labelled precursors indicated that the photobionts produce from CO₂ glucose or sugar alcohols (e.g. ribitol and arabitol) which are then transferred to the mycobionts. In the fungi, these compounds are believed to be converted into mannitol serving as the carbon and energy source in the downstream metabolic processes. Recent methodological developments in spectroscopy and “systems biology” now enable a concise analysis of the metabolite profiles, networks and fluxes by non-targeted quantitative approaches. In this review, we summarize the current knowledge about lichen metabolism and report on the potential of the advanced methods to reinvestigate lichen chemistry and metabolism on a quantitative basis.