Honey bee stock mediates the gut microbiome response to diet

Beekeepers commonly supplement their honey bee (Apis mellifera L.) colonies with artificial pollen substitutes to mitigate the risk of nutritional stress and support colony growth. Microalgae are emerging as nutritionally rich and immune-stimulating feed ingredients for apicultural use, though their impacts on the gut microbiome are not yet well understood. Here, we carried out a cage study to investigate the gut microbiome response of two genetically distinct honey bee stocks (Pol-line and Russian) to spirulina (Arthrospira platensis) and Chlorella (Chlorella vulgaris) diets. Pollen served as the positive control and a sugar-only diet served as the negative control. DNA extracted from pooled abdomen samples of eight-day-old bees underwent PacBio HiFi amplicon sequencing targeting the full-length 16S rRNA gene to capture strain-level diversity of gut bacteria communities. All non-pollen diets reduced strain richness of several key bacterial genera and overall alpha diversity. Similarly, beta diversity analyses revealed separation and differential dispersion between the communities of pollen-fed bees and others. However, significant interaction effects with stock suggest differential volatility of the gut microbiome between Pol-line and Russian bees in response to the spirulina and sugar-only diets. Notably, Bartonella proliferated more readily in Russian bees in response to the sugar diet than in Pol-line bees, suggesting better adaptation to the dietary shifts reflecting winter conditions. Our findings contribute to a stronger understanding of how an animal host’s genetic background influences diet-induced shifts in the gut microbiome and may allow for the development of feeding regimes tailored to specific honey bee stocks.