[Gut fungal community composition and metabolic potential in honeybees and bumblebees]

Honeybees and bumblebees are key agricultural pollinators, whose gut microbiota play critical roles in host nutrient metabolism, immune regulation, and environmental adaptation. While gut bacterial communities have been extensively studied, the composition and ecological functions of gut fungi remain poorly understood. This study aims to fill this knowledge gap by systematically characterizing the diversity, phylogeny, and functional potential of pollinator gut fungi. In this study, we analyzed the gut fungal community structures of four pollinator species-Apis cerana, Apis mellifera, Bombus impatiens, and Bombus vosnesenskii-based on publicly available internal transcribed spacer (ITS) amplicon sequencing data. Additionally, we conducted whole-genome analyses of 25 cultivable fungal strains isolated from the gut of Apis spp. and Bombus spp. individuals collected from the Beijing Baihuashan National Nature Reserve. The results showed that Ascomycota was the dominant fungal phylum across all hosts, with significant differences in fungal diversity and community composition among host species. Phylogenetic analysis indicated high taxonomic consistency of isolated strains at the genus and species levels, along with diverse genome architectures. Functional annotations revealed that gut fungi were broadly involved in carbohydrate metabolism, cellular structure maintenance, and signal transduction. Notably, Metschnikowia strains exhibited significant enrichment in CAZyme families, particularly glycoside hydrolases (GH) and glycosyltransferases (GT). In addition, some strains possess biosynthetic gene clusters for secondary metabolites, such as nonribosomal peptide synthetase (NRPS) and β- lactones, which suggested potential roles in microbial competition and fungus-host interactions. This study uncovers the diversity and functions of fungal communities in bee guts, enriching our understanding of insect microbiomes and providing a theoretical foundation for pollinator health maintenance and microbiota-targeted interventions.