Dietary supplementation with phytochemicals improves diversity and abundance of honey bee gut microbiota

Authors: GELDERT, CHRISTINA - Colorado State University; ABDO, ZAID - Colorado State University; STEWART, JANE - Colorado State University; Seshadri, Arathi

Submitted to: Journal of Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/10/2020
Publication Date: 4/12/2021
Citation: Geldert, C., Abdo, Z., Stewart, J., Seshadri, A.H. 2021. Dietary supplementation with phytochemicals improves diversity and abundance of honey bee gut microbiota. Journal of Applied Microbiology. 130(5):1705-1720. https://doi.org/10.1111/jam.14897.
DOI: https://doi.org/10.1111/jam.14897

Interpretive Summary: Honey bees continue to face challenges resulting from habitat loss related compromises to nutrition, exposure to agrochemicals and devastating pests and pathogens. Honey bees depend on plants for their nutritional needs. Pollen and nectar produced by plants, in addition to protein, lipids and carbohydrates, provide bees with a wealth of micronutrients including phytochemicals such as flavanols and alkaloids. Continued habitat degradation and compromised access to quality nutrition, has negatively impacted gut microbial flora and overall health of bees. Earlier studies demonstrated that phytochemical supplementation to worker bees increased their longevity and pathogen tolerance. Here, we provide evidence showing that dietary supplementation with pollen and nectar phytochemicals such as caffeine, gallic acid, p-coumaric acid, or kaempferol, can improve diversity and abundance of the gut microbiome. It is important to note that the gut microbiota composition and abundance exhibit temporal stabilization post-supplementary diet.

Technical Abstract: Aim: To determine the impact of supplementing honey bee (Apis mellifera) diets with four plant-derived beneficial phytochemicals (caffeine, gallic acid, p-coumaric acid, or kaempferol) on the diversity and abundance of the gut microbiome. Methods and Results: Worker honey bees from three source colonies were fed ad libitum with a diet consisting of 25 ppm of the individual phytochemical + 20% (w/v) sucrose and collected at 3 and 6 days. Next Generation sequencing was performed on entire alimentary tracts for bacterial 16S and fungal ITS regions. Dietary supplementation with phytochemicals in general foster diversity in gut microbiota but the pattern of effects differed between phytochemicals. There was a clear temporal stabilization of the bacterial community as evident from comparison of baseline bacterial diversity with that at 3-day and 6-day time-points. Bacterial and fungal communities in the gut responded differently to phytochemical supplementation. When compared to a sucrose-only diet, all phytochemical treatments displayed increased abundance of most represented bacterial taxa. Conclusions: Phytochemical supplementation promotes gut microbial diversity and abundance. Proliferation of Snodgrassella spp. suggests the potential for phytochemicals to improve defense against the ectoparasite, Varroa destructor. Increased relative abundance of Lactobacillus spp., associated with longevity, can explain previously reported increased longevity in bees supplemented with these phytochemicals. Significance and Impact of Study: This is the first report of microbiota analysis following phytochemical supplementation in honey bees. This can be used in medical management and husbandry to inform probiotic use and standardize dosages of feed supplements for improvement of honey bee health.