Symbiotic Enterococcus faecalis potentiates viral pathogenesis via fructose-1,6-bisphosphate-mediated insect gut epithelial damage.

Chinese sacbrood virus (CSBV) is highly lethal to Asian honey bee (Apis cerana) larvae. While gut symbionts are known to regulate viral infection, their role in CSBV pathogenesis remains poorly understood. Through 16S rRNA gene sequence analysis of the field-collected honey bees, we found that the larvae had a substantially higher relative abundance of Enterococcus than pupae or adults. Metagenome sequencing analysis of field-collected larvae demonstrated that CSBV infection significantly induced more than 45-fold enhancement in the abundance of Enterococcus faecalis, an opportunistic pathogen implicated in the development of purulent cystic lesions. In microbiota-free (MF) bees, colonization with E. faecalis markedly suppressed phospholipid metabolism and elevated levels of 4-guanidinobutyric acid and fructose-1,6-bisphosphate (FBP). These metabolic changes were associated with cytotoxicity and apoptosis, which worsened goblet cell damage and thereby facilitated CSBV infection, as indicated by metabolomics and pathological section analysis. Crucially, exogenous FBP administration directly enhanced cytotoxicity and apoptosis of gut in CSBV-infected MF bees, mirroring the CSBV susceptibility was mediated by E. faecalis. Our study unveiled a symbiotic bacteria's involvement in promoting RNA virus infection through metabolic reprogramming and epithelial barrier dysfunction, providing new insights into host-microbe-virus interactions in pollinators.