Gut microbiome response to protective treatments against Nosema sp. Infection in the honey bee (Apis mellifera) gut microbiome

Background: Honey bees (Apis mellifera) are essential pollinators of various crops with high economic value and their pollination services can be compromised by disease. Nosemosis is an infection of the honey bee midgut with the microsporidium Nosema sp. which is found among managed colonies across the globe. This can affect the honey bee gut microbiome, a community of microorganisms known to contribute to bee health and immunity.

Objective: To examine the effect of different commercial protective treatments on the honey bee gut microbiome infected with Nosema sp..

Methods: The honey bee gut microbiome of winter bees maintained in cages was analyzed using 16S rRNA amplicon sequencing to determine the microbial composition at three time points: pre-treatment (TP1), post-treatment (TP2), and post-infection with Nosema sp. (TP3). Amplicon sequence variants (ASVs) were identified at each time point using the bioinformatics platform QIIME2 to determine the microbial composition of the gut.

Results: Gut microbiome genera with high representation included Lactobacillus spp., Gilliamella spp., Snodgrasella spp., as well as Bartonella spp. and Commensalibacter spp.. Interestingly, ASVs of the family Enterobacteriaceae were also detected. Beta-diversity analysis revealed a shift in the relative abundance of the microbial community over time while in cages, with a significant decrease in the proportion of Lactobacillus spp. and an increase in Enterobacteriaceae, particularly at TP3. At this post-infection time point, the Nosema-infected group had a different microbiome profile than the negative control group, indicating that Nosema sp. infection caused dysbiosis. In particular, the relative abundance of Enterobacteriaceae was significantly increased in infected bees compared to non-infected bees. Treatment with oxytetracycline, an antibiotic used to treat bee brood diseases, and the feeding stimulant Honey B Healthy, appeared to have a protective effect and resulted in a microbiome profile with increased similarity to the profile of non-infected bees. In summary, our findings show that Nosema sp. infection in caged honey bees results in bacterial dysbiosis. Certain treatments, however, can contribute a protective effect and help maintain the natural composition of the honey bee gut microbiome.