Microbial ecology of European foul brood disease in the honey bee (Apis mellifera): towards a microbiome understanding of disease susceptibility

Authors: FLOYD, AMY - University Of Arizona; Mott, Brendon; MAES, P - University Of Arizona; COPELAND, D - University Of Arizona; MCFREDERICK, Q.S. - University Of California; Anderson, Kirk

Submitted to: Insects
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/18/2020
Publication Date: 8/20/2020
Citation: Floyd, A.S., Mott, B.M., Maes, P., Copeland, D., McFrederick, Q., Anderson, K.E. 2020. Microbial ecology of European foul brood disease in the honey bee (Apis mellifera): towards a microbiome understanding of disease susceptibility. Insects. 11(9):555. https://doi.org/10.3390/insects11090555.
DOI: https://doi.org/10.3390/insects11090555

Interpretive Summary: European honey bees are beneficial insects that provide essential pollination services for agriculture and ecosystems worldwide. Modern commercial beekeeping is faced with a variety of pathogenic and environmental stressors often confounding attempts to understand recent colony loss. European foulbrood (EFB) is a larval disease whose causative agent, Melissococcus plutonius, has received limited attention due to methodological challenges in the field and laboratory. Here we improve the experimental and informational context of larval disease with the end goal of developing an EFB management strategy. We used genetic barcoding to identify bacteria (microbiome) associated with larval disease transmission, isolated a variety of M. plutonius strains, determined the concentration of M. plutonius that killed 100% and 50% of larvae in the lab setting, and explored the potential for probiotic treatment of EFB disease. The larval microbiome was a low diversity environment similar to honey, while worker mouthparts and stored pollen contained significantly greater bacterial diversity. The effect of M. plutonius on larval mortality varied markedly by bacterial strain and amount of introduced bacteria. In the context of EFB infection in the laboratory setting, our chosen probiotic strain did not have a significant effect on larval survival. We discuss the importance of positive and negative controls for laboratory studies of the larval microbiome and disease.

Technical Abstract: European honey bees (Apis mellifera) are beneficial insects that provide essential pollination services for agriculture and ecosystems worldwide. Modern commercial beekeeping is faced with a variety of pathogenic and environmental stressors often confounding attempts to understand recent colony loss. European foulbrood (EFB) is a larval disease whose causative agent, Melissococcus plutonius, has received limited attention due to methodological challenges in the field and laboratory. Here we improve the experimental and informational context of larval disease with the end goal of developing an EFB management strategy. We sequenced the bacterial microbiome associated with larval disease transmission, isolated a variety of M. plutonius strains, determined their virulence against larvae in vitro, and explored the potential for probiotic treatment of EFB disease. The larval microbiome was a low diversity environment similar to honey, while worker mouthparts and stored pollen contained significantly greater bacterial diversity. Virulence of M. plutonius against larvae varied markedly by strain and inoculant concentration. In the context of EFB infection in vitro, our chosen probiotic strain did not have a significant effect on larval survival. We discuss the importance of positive and negative controls for in vitro studies of the larval microbiome and disease.