Development of the sexual reproductive cycle of Xanthophyllomyces dendrorhous

Conditions inducing the development of holobasidia with terminal basidiospores in wild-type and astaxanthin mutant strains of Xanthophyllomyces dendrorhous were reexamined. Important factors for the development of holobasidia were the incubation temperature and the medium composition. A temperature of 9 degrees C was demonstrated to enhance holobasidia formation. Minimal growth medium with glucose as sole carbon source at concentrations between 80 and 120 mM, and ammonium nitrate with concentrations of 28 mM gave optimal results. A period of 20 or more days was needed for the formation of holobasidia with basidiospores. Additionally, mutant strains of X. dendrorhous were observed to have different abilities to produce holobasidia and strains obtained after protoplast fusion, which have been called fusant in this study, to have an increased capacity to form holobasidia.