Yeasts in pollen collected by honey bees in Belgium. Yeasts in honey bee pollen

Honey bees (Apis mellifera) not only collect and store nectar, but also pollen as essential part of their food. Pollen stored by bees undergoes a mixed lactic acid fermentation marked by the presence of lactic acid bacteria and yeasts and resulting in bee bread. In particular the nutrition of queens and immature stages of bees relies on pollen as source of proteins, lipids, vitamins and minerals. The role of microorganisms for the biochemical conversions during pollen storage is not yet agreed upon and the suggested possibilities include the selection of environmental microorganisms by the bee bread properties, pollen preservation, nutrient enrichment, pre-digestion, or a combination of several effects. The presented study aimed to improve the understanding of the yeasts encountered during the conversion of bee-collected pollen to bee bread.Most of the detected yeast diversity was concentrated in three phylogenetic groups, namely members of the Starmerella and Metschnikowia clades, as well as the genus Zygosaccharomyces. The abundance of yeasts decreased with the duration of bee bread storage. Yeasts of the Starmerella clade dominated fresh bee bread, while almost exclusively Zygosaccharomyces members were isolated from aged bee bread. Candida apis (Starmerella clade), known only from a strain isolated from a bee trachea in the United Kingdom, was the most frequent and abundant species in fresh bee bread. Yeasts from the bee’s honey stomach and from bee-collected pollen pellets were dominated by Metschnikowia spp. and showed low numbers of Starmerella and Zygosaccharomyces members. The distinctive communities from bee-collected pollen over fresh bee bread to aged bee bread suggest a non-random distribution of these yeasts. Further work is needed to clarify the roles of certain groups and species of yeasts for bee nutrition.