Lichen Biomass: A Perspective on Polymer Chemistry

Lichens can be recognized as a symbiotic partnership due to an association between a fungus and one or more chlorophyll partners (algae or cyanobacteria), leading to a thallus. The lichen-associated fungi comprise ascomycetes and basidiomycetes, whereas the algae involved in this association are chlorophytes or cyanobacteria. This association process contributes to substantial evolutionary radiation of the fungus and allows its photobiont partners to grow under severe conditions. Lichen species are estimated to count between 18,000 and 20,000 worldwide, of which less than 100 lichen species have been chemically characterized regarding their polysaccharide composition. Therefore, the lichen polymeric biomass is commonly from a fungal origin, in which α-glucans, β-glucans, and galactomannans can be isolated in large yields. Furthermore, due to their chemotaxonomic importance, lichen polysaccharides based on glucan and galactomannan types have been pointed out. Thus, several studies have reported the biological effects of lichen polysaccharides, in particular those regarding the antitumor, immunomodulating, antiviral, and memory-enhancing effects. The current chapter summarizes the knowledge of lichen polysaccharides’ structural characteristics and the vibrational spectroscopic techniques used to elucidate their chemical composition.