Culture studies on the mycobiont isolated from Parmotrema reticulatum (Taylor) Choisy: metabolite production under different conditions

A strain of the lichen mycobiont isolated from a thallus of Parmotrema reticulatum was cultured axenically on different media. The morphology, anatomy, growth of the colonies, and metabolite production were studied. The isolated fungal colonies developed well and showed a remarkable morphogenetic capacity on most of the assayed solid media, e.g., malt extract 2%-yeast extract 0.2% (MEYE), malt extract 1%-yeast extract 0.4%-sucrose 10% (MY10), and the original Lilly & Barnett medium (LB). The identity of the isolated fungus was confirmed by its ITS rDNA-sequence. Atranorin, the major cortical lichen depside, was produced when the colonies were grown over 5 and 10 months on solid LB medium, combined with a dessication treatment. Atranorin was identified by matching of UV spectra obtained from HPLC running and a reference substance in a spectrum library. Colonies grown on MEYE and MY10 with a dessication treatment did not produce any lichen secondary metabolite. Mycobionts grown for 5 months on solid MEYE without a dessication treatment produced triacylglycerides as the major metabolites, and the fatty acids were characterized as their methyl esters. Analysis by TLC and HPLC-DAD of extracts of colonies grown on LB and MY10 without dessication revealed that the typical secondary compounds of the natural lichen were not produced. The major metabolites of the natural lichen thallus were identified by chromatographic and spectroscopic methods.