Morphological and molecular characterization of yeasts from the genus \kur{Zygosaccharomyces} associated with honey bees

Beekeeping is one of the oldest fields of human activity. A key role in this field is played by the honey bee (Apis mellifera), which is also an important pollinator of agricultural crops and wild plants. Although bees have evolved defense mechanisms during their long evolution against a variety of external influences, bee´s existence is currently threatened by several factors. An interesting way for increasing the immunity of the bee colony seems to be the honey bee microbiome. Honey bee microbiome is the main focus of this thesis, with a practical part focused on yeasts of the genus Zygosaccharomyces. Twenty samples/strains of the yeasts were isolated from the intestines of bee larvae, pollen baskets, and pollen on selected culture media. Based on sequencing of the D1/D2 region of the large ribosomal DNA subunit, three species of the genus Zygosaccharomyces were identified in these twenty samples: Z. rouxii, Z. favi and Z. mellis. Four pairs of primers were also designed within the ITS region and can be an alternative or complement to the molecular characterization of isolated yeast strains based on another marker region of DNA. All primers were evaluated as specific for Z. rouxii species. Using one pair of primers, the part of ITS region was also amplified in the species Z. mellis. According to this, these primers could also be used to identify this species as well. The last part of this work is the determination of ergosterol production in yeast biomass by HPLC. Ergosterol is produced by the Zygosaccharomyces yeasts and it plays an important role in the development of the bee brood. It was found in this thesis, that ergosterol levels in yeasts are not uniform and also do not correlate with biomass production. The highest production of ergosterol was found in the species Z. mellis, which is a sample obtained from pollen. The outputs of this work provide a new perspective on the colonization of the intestinal microbiota of bees and also offer potential significance for the future, especially in the application of yeast as a source of ergosterol for developing larvae