A high-throughput sequencing survey characterizing European foulbrood disease and Varroosis in honey bees

Authors: Anderson, Kirk; Copeland, Duan; Erickson, Robert; FLOYD, A. - University Of Arizona; MAES, P. - University Of Arizona; Mott, Brendon

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/12/2023
Publication Date: 1/12/2023
Citation: Anderson, K.E., Copeland, D.C., Erickson, R.J., Floyd, A., Maes, P., Mott, B.M. 2023. A high-throughput sequencing survey characterizing European foulbrood disease and Varroosis in honey bees. Scientific Reports. 13. Article 1162. https://doi.org/10.1038/s41598-023-28085-2.
DOI: https://doi.org/10.1038/s41598-023-28085-2

Interpretive Summary: Critical for pollination in agricultural and ecosystems, modern commercial honey bees (Apis mellifera) are faced with a variety of pathogenic and environmental stressors that often result in colony or crop loss. One pathogenic stressor is the bacterial larval disease European foulbrood (EFB) attributed to the bacterium Mellisococcus plutonius. However, many disease phenotypes visually classified as EFB do not contain M. plutonius based on microscopy and molecular markers, and are referred to as idiopathic. Here we improve the informational context of the larval disease microbiome with the end goal of developing diagnoses and management strategies for EFB and EFB-like disease. We used next generation sequencing and qPCR to detail the bacteria found in visibly healthy and diseased larvae from six different apiaries in the state of Illinois, USA. A state apiary inspector diagnosed the disease in all six apiaries as EFB according to collective morphological phenotype. At five of the six apiaries, Mellisococcus plutonius dominated the larval disease microbiome, showing associations with three different firmicutes dependent on apiary. At the sixth site, the diseased larvae were uniquely described as “melty, sunken and deflated”, and the resulting microbiota indicates a novel disease state involving Serratia marcescens that corresponds to the symptoms of idiopathic brood disease syndrome.

Technical Abstract: As essential pollinators of ecosystems and agriculture, honey bees (Apis mellifera) are host to a variety of pathogens that result in colony loss. Two highly prevalent larval diseases are European foulbrood (EFB) attributed to the bacterium Melissococcus plutonius, and Varroosis wherein larvae can be afflicted by one or more paralytic viruses. Here we used high-throughput sequencing and qPCR to detail microbial succession of larval development from six diseased, and one disease-free apiary. The disease-free larval microbiome revealed a variety of disease-associated bacteria in early larval instars, but later developmental stages were dominated by beneficial symbionts. Microbial succession associated with EFB pathology differed by apiary, characterized by associations with various gram-positive bacteria. At one apiary, diseased larvae were uniquely described as “melting and deflated”, symptoms associated with Varroosis. We found that Acute Bee Paralysis Virus (ABPV) levels were significantly associated with these symptoms, and various gram-negative bacteria became opportunistic in the guts of ABPV afflicted larvae. Perhaps contributing to disease progression, the ABPV associated microbiome was significantly depleted of gram-positive bacteria, a likely result of recent antibiotic application. Our results contribute to the understanding of brood disease diagnosis and treatment, a growing problem for beekeeping and agriculture worldwide.