Ecology of pollen storage in honey bees: sugar tolerant yeast and the aerobic social microbiota

Authors: Anderson, Kirk; Mott, Brendon

Submitted to: Insects
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/5/2023
Publication Date: 3/8/2023
Citation: Anderson, K.E., Mott, B.M. 2023. Ecology of pollen storage in honey bees: Sugar tolerant yeast and the aerobic social microbiota. Insects. 14(3). Article 265. https://doi.org/10.3390/insects14030265.
DOI: https://doi.org/10.3390/insects14030265

Interpretive Summary: Honey bees colonies are resource rich, and filled with vast microbial diversity, generating a constant battle to control microbial growth throughout the hive. Honey is relatively sterile in comparison with beebread; comprised of pollen mixed with honey and worker head gland secretions. Beebread contains a small but diverse microbiota and is a reservoir for core gut bacteria, sugar-tolerant yeasts, fungal pathogens and bacterial opportunists that populate or afflict both larval and adult stages. The microbes of the social environment as defined by BEExact are shared between beebread, honey, royal jelly and the anterior gut segments and mouthparts of both queens and workers. Here we used two methods to quantify fungi and bacteria tinvestigating changes in beebread by both storage time and season. Over the early beebread maturation period, pH and water availability decrease significantly. Following an initial drop in microbial abundance from corbicular pollen to day one, both yeasts and bacteria multiply rapidly during day two. Then at 3-7 days, yeasts and bacteria decline but yeasts decline much less rapidly than bacteria in the increasingly hostile environment. The sugar tolerant yeasts were significantly more resilient to decreased water availability and increased pH than were bacteria. This work contributes to our growing understanding of host-microbial interactions in the honey bee gut and colony environment, and the effect of pollen storage on microbial communities, nutrition and bee health.

Technical Abstract: Honey bee colonies are resource rich and densely populated, generating a constant battle to control microbial growth. Honey is relatively sterile in comparison with beebread: a food storage medium comprising pollen mixed with honey and worker head-gland secretions. Within colonies, the microbes that dominate aerobic niches are abundant throughout social resource space including stored pollen, honey, royal jelly, and the anterior gut segments and mouthparts of both queens and workers. Here, we identify and discuss the microbial load in stored pollen associated with non-Nosema fungi (primarily yeast) and bacteria. We also measured abiotic changes associated with pollen storage and used culturing and qPCR of both fungi and bacteria to investigate changes in stored pollen microbiology by both storage time and season. Over the first week of pollen storage, pH and water availability decreased significantly. Following an initial drop in microbial abundance at day one, both yeasts and bacteria multiply rapidly during day two. Both types of microbes then decline at 3–7 days, but the highly osmotolerant yeasts persist longer than the bacteria. Based on measures of absolute abundance, bacteria and yeast are controlled by similar factors during pollen storage. This work contributes to our understanding of host–microbial interactions in the honey bee gut and colony and the effect of pollen storage on microbial growth, nutrition, and bee health.