Chapter 5 - Secondary metabolites of lichens and their application

Abstract

Secondary metabolites are a class of outwardly directed differentiation products of regular cellular metabolism that can operate as chemical messengers across organisms and species. They are molecules largely engaged in the maintenance/homeostasis of the organism. Secondary metabolites influence health-maintenance functions. Utilizing secondary metabolites has proven to be particularly successful in detecting some of the most prevalent food-spoilage fungus, including Penicillium species, Aspergillus species, and Fusarium species. Secondary products are uncommon, low-molecular-weight molecules that are structurally like primary metabolites but have a more restricted distribution than primary metabolites. Lichens are the natural result of a partnership between fungi (the Mycobionts’ partner) and algae (the host of the association). The stability of the secondary metabolites of lichens separates them from other species. Lichens can be both beneficial and hazardous to humans, depending on the location. They assist humanity in numerous ways, including feed and food, medicine, and industrial applications. In France, several lichens are used to make chocolates and pastries, while others are used medicinally. Curry powder made from Parmelia species can be found in Indian cuisine, while Endocarpon miniatum is used as a vegetable in Japan and Evernia prunastri is used to make bread in Egypt. The presence of lichenin, a polysaccharide, in Ramalina fraxinea, R. fastigiata, Evernia prunastri, and Lobaria pulmonaria lichens enables their use as animal feed. Parmelia saxatilis and Parmelia perlata are employed in the treatment of dyspepsia and epilepsy, respectively. Cladonia pyxidata is used to cure whooping cough, Xanthoria parietina is used to treat jaundice, and Pertusaria, Cladonia, and Cetraria are used to treat a variety of conditions. Ochrolechia androgyna and Ochrolechia tartaria are two plants that yield red and purple colors, respectively. Species of Ramalina and Evernia are used to extract the essential oils used to produce cosmetic soap. Some lichens, such as Amphiloma and Cladonia, parasitize mosses and, if left unchecked, can entirely decimate moss colonies. Some secondary compounds produced by lichens, such as anthraquinone pigments, are commonly present in both lichens and free-living fungi. The low levels of bacterial production allow for rapid mutation, selection of resistant strains, and horizontal transmission of resistance genes. Extracts of Usnea ghattensis, Parmotrem pseudotinctorum, Hypogymnia physodes, Lasallia pustulosa, and Parmelia caperata exhibited antioxidant activity. The majority of lichen species are terrestrial, whereas only a handful are found in the ocean.