Microbiome of honey bee corbicular pollen: Factors influencing its structure and potential for studying pathogen transmission

Honey bees are exposed to a diverse variety of microbes in the environment. Many studies have been carried out on the microbiome of bee gut, beebread, and flower pollen. However, little is known regarding the microbiome of fresh corbicular pollen, which can directly reflect microbes acquired from the environment. Moreover, although evidences have suggested that floral resources in general can affect the bee-acquired microbes, whether specific forage plants affect the composition of these microbes is still unclear. Here, we characterized both the microbiome and plant composition of corbicular pollen in collection seasons over two years from six hives using 16S rRNA gene and ITS2 metabarcoding. The results reveal temporal changes in the microbiome and plant composition in corbicular pollen, which was influenced by environmental factors and the choice of forage plants. We identified several co-occurrences between plant and bacterial genera, indicating specific plant-microbe interactions. Many Spiroplasma species with various insect hosts, including a honey bee pathogen Spiroplasma melliferum, were shown to positively correlate with Rubus, suggesting this plant genus as an important node for microbial transmission. Overall, we demonstrated the potential of corbicular pollen for studying the transmission of microbes, especially pathogens. This framework can be applied in future research to explore the complicated pollinator-microbe-plant network in different ecosystems.