Nosema ceranae infection enhances Bifidobacterium spp. abundances in the honey bee hindgut

Nosema ceranae has become the dominant Nosema pathogen in the honey bees, Apis mellifera. It primarily infects and reproduces in midguts and reproduced N. ceranae spores travel to hindguts and leave hosts with feces. Hindguts have structural support for bacterial symbionts and biofilms, which harbor the densest bacteria of the entire bee. Although some bacteria were inhibitory to N. ceranae in the laboratory trials, N. ceranae disease is not apparently hurdled by hindgut bacteria. We suspected N. ceranae infection may affect hindgut bacteria populations to favor the spore survival. In this study, hindgut bacterial microbiomes of defecated foragers were analyzed using a pyrosequencing method. The results suggested Bifidobacterium spp. abundances were significantly and positively associated with N. ceranae infection. To confirm the association in a larger sample size, we used caged bees and qPCRs that quantify bifidobacteria and lactobacteria. The same association was found in emptied hindgut samples, but not significant in feces samples. Bifidobacteria in feces might increase when bifidobacteria on hindguts are significantly enhanced by N. ceranae infection. Although we have not identified the specific causes and mechanisms of this association, the results suggested that indigenous Bifidobacterium spp. in honey bee hindguts may have no prevention effects on N. ceranae disease.