Líffræðifélag Íslands - biologia.is
Líffræðiráðstefnan 2019

Erindi/veggspjald / Talk/poster E77

Biochirality of usnic acids in the lichenized fungal family Parmeliaceae

Höfundar / Authors: Maonian Xu (1), Starri Heidmarsson (2), Elin S. Olafsdottir (1)

Starfsvettvangur / Affiliations: 1. Háskóli Íslands, 2. Náttúrufræðistofnun Íslands

Kynnir / Presenter: Maonian Xu

Usnic acid is one of the most ubiquitous lichen compounds present in lichen cortex. They could constitute as high as 8% dry thallus weight. (+)-usnic acid has a more pronounced antimicrobial activity, while the (-)-usnic acid is a more potent phytotoxin. Despite such high contents and pronounced bioactivities, the distribution of isomers has not been explored in an evolutionary and ecological context, which is mainly due to the lack of chemical analytic methods and sampling efforts. The current study aimed to develop an analytical method characterizing the ratio of usnic acid isomers in the lichenized fungal family Parmeliaceae (59 specimens of seven genera), and to see if their production has any phylogenetic and ecological implications. A UPLC-PDA-MS method was developed to quantify the total content of usnic acid. Then the acid was fractionated using a preparative HPLC method, and isomeric ratio was determined using a chiral HPLC method. Phylogenetic relationship of lichenized fungi was estimated using a multi-loci analysis. Our results show that usnic acid could account for ca. 0.2-4.8% dry-weight lichen thalli. The production of usnic acid isomers tend to be intra- specifically homogeneous with one isomer as the predominant and the other minor or absent. Ubiquitous terricolous taxa (e.g. genera Alectoria and Flavocetraria) mainly produce (-)-usnic acid, and the epiphytic genera (e.g. Usnea and Evernia) mainly produces (+)-usnic acid. Our preliminary results indicate that terricolous lichens tend to produce mainly phytotoxic (-)-usnic acid, which may favor their colonization on the ground by competing with plants, while epiphytes produce mainly (+)-usnic acid which could aid in competing with other epiphytic microorganisms.