Maia Biwersi, Maonian Xu and Elin Olafsdottir
Introduction: Chiral compounds of natural origins usually occur in one major enantiomeric form with exceptions were both enantiomers are produced. Enantiomers may have drastically different bioactivity and toxicological profiles and to figure out their enantioselective biosynthesis could have profound pharmaceutical and biotechnological implications. Usnic acid (UA) enantiomers in lichens are potent antimicrobial compounds, while their enantiomeric composition and biosynthesis has not been investigated. This study focuses on the lichenized fungal family Cladoniaceae and aims to characterize the biosynthesis of usnic acid enantiomers in this family.
Methods and data: Determination of UA enantiomers is performed using a validated chiral high performance liquid chromatography (HPLC) method. Fungal phylogenetic tree is constructed by concatenating four fungal loci, i.e. nrITS, MCM7, mtSSU and RPB2, which are amplified using polymerase chain reactions with newly designed mycobiont-specific primers. The phylogenetic relationship of the annotated polyketide synthase genes is analyzed.
Results: The contents of UA enantiomers are quantified by the chiral HPLC, accounting for 0.1 to 4% lichen dry weights. There is a strong phylogenetic pattern for enantiomeric biosynthesis: the reindeer lichen clade is producing the (+)-UA, while the other clades the (-)-UA. Phylogenetic analysis of biosynthetic genes also revealed the same pattern.
Conclusions: The current study revealed the biosynthetic pattern of UA enantiomers in the family Cladoniaceae, and key variations in the biosynthetic genes have been identified.
