The Impact of Vairimorpha (Nosema) ceranae Natural Infection on Honey Bee (Apis mellifera) and Bee Bread Microbiota

Honey bees face new challenges, ranging from climate crisis to emerging pathogens such as Vairimorpha (Nosema) ceranae that synergistically cause a syndrome designated as colony collapse disorder (CCD). This study employed a metataxonomic approach in order to investigate if V. ceranae affects gut microbiota (bacteria and fungi) of adult A. mellifera honey bees as well as microbiota of bee bread (BB) stored in colonies demonstrating severe V. ceranae infection (spore counts >2,500,000 per bee) as compared with colonies exhibiting very low spore counts (<40,000 per bee). Alpha-diversity analysis revealed an overall decrease in microbial diversity reflected by number of observed unique operating taxonomic units (OTUs) regarding both bacteria and fungi in honey bee and Beta Beta samples. Further analysis demonstrated that Podosphaera spp. were absent in BB samples collected from colonies with high spore counts, while relative abundance of Blumeria spp. was significantly decreased. Interestingly, relative abundance of Rosenbergiella spp. was increased in BB samples collected from colonies with high spore counts. The reason for these findings remains elusive. Although further research is warranted, overall reduced microbial diversity and relative abundance of certain microbial groups may serve as biomarkers of colony collapse.