The microbiome and gene expression of honey bee workers are affected by a diet containing pollen substitutes

Authors: POWELL, ELIJAH - University Of Texas At Austin; Lau, Pierre; RANGEL, JULIANA - Texas A&M University; ARNOTT, RYAN - University Of Texas At Austin; DEJONG, TYLER - University Of Texas At Austin; MORAN, NANCY - University Of Texas At Austin

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/9/2023
Publication Date: 5/19/2023
Citation: Powell, E.J., Lau, P.W., Rangel, J., Arnott, R., Dejong, T., Moran, N.A. 2023. The microbiome and gene expression of honey bee workers are affected by a diet containing pollen substitutes. PLOS ONE. https://doi.org/10.1371/journal.pone.0286070.
DOI: https://doi.org/10.1371/journal.pone.0286070

Interpretive Summary: Poor nutrition is a leading cause of honey bee colony mortality in the U.S. It is therefore critical to supplement colonies with nutrition and understand its effects on bee health. We tested artificial pollen-free diets and compared its effects on the honey bee gut microbiome to bees fed natural pollen. We show that honey bees fed a pollen-free artificial diet, despite having similar protein and lipid contents, reduced individuals of microbial diversity. This correlated to a reduced expression of genes for development and ability to bacterial infection compared to bees fed natural pollen. This information will help us better address problems associated with poor nutrition in honey bees and how beekeepers can manage nutritional stress.

Technical Abstract: Bacterial species within the honeybee gut microbiota are specialized to digest components of the complex outer coat of pollen, which is the primary source of dietary protein. However, during periods of reduced availability of floral pollen, supplemental protein sources are frequently provided to managed honeybee colonies. The crude proteins in these supplemental feeds are typically byproducts from food manufacturing and rarely include pollen. Our study showed that a simplified pollen-free diet formulated to resemble the macronutrient profile of a monofloral pollen source resulted in larger microbial communities with reduced diversity, reduced evenness and reduced levels of potentially beneficial hive-associated bacteria. Further, the pollen-free diet sharply reduced the expression of genes central to honeybee development. In subsequent experiments, we showed that these shifts in gene expression may be linked to colonization by the gut microbiome. Lastly, we demonstrated that, for bees inoculated with a defined gut microbiota, those raised on an artificial diet were less able to suppress infection from a bacterial pathogen than those fed pollen.