Culture studies on the mycobiont of Caloplaca erythrantha (Tuck.) Zahlbr. (Teloschistaceae): high production of major lichen secondary metabolites

Abstract

AbstractA strain of the lichen mycobiont of Caloplaca erythrantha, isolated from ascospores, was cultured axenically on different solid media. Four of the media employed supported the development of colonies and production of the two major lichen secondary metabolites. These media were: BMYE (mannitol 2%, yeast extract 0·1%, in Bold's basal medium); MEYE (malt extract 2%, yeast extract 0·2%, in distilled water); Hamada's MY10 (malt extract 1%, yeast extract 0·4%, sucrose 10%, in distilled water); and the new BMRM (Bold mannitol rich medium, mannitol 5·3%, malt extract 1%, yeast extract 0·4% in Bold's mineral medium). Percentages refer to final medium volume. The fungal colonies developed well on the four media and produced emodin and 7-chloroemodin, the major secondary compounds of the lichen apothecia. Crystals deposited richly on the external surface of the hyphae, as observed with an optical microscope. The two anthraquinones were purified from the lichen thallus, apothecia and cultured mycelia, and identified by chromatographic (TLC, HPLC) and spectroscopic (NMR, MS) methods. The analysis of lichen apothecia revealed the presence of emodin (0·90% w/w) and 7-chloroemodin (0·56% w/w), whereas colonies cultured for five months generally produced higher percentages than the lichen: 1·72% emodin and 0·30% 7-chloroemodin on BMYE; 0·21% and 0·95% on MEYE; 7·82% and 7·48% on MY10; and 11·70% and 10·80% on BMRM. These results show that the production of both anthraquinones was promoted significantly in mycobiont cultures with high concentrations of the carbon sources sucrose or mannitol, with a higher effect being observed with the latter.