Study Models For The Interaction Between Intestinal Microbiota And Viral Infection In Fish

In China,aquaculture is a big industry which provides people a large amount of high-quality protein.Virus diseases are big threat to the aquaculture industry.Traditional treatments cannot effectively kill the virus and control the their spread.The intestinal microbiota has be implicated to be involved in the interaction of the host and virus,by regulating the anti-viral immunity.Accordingly,some probiotics showed efficiency in controlling the infection and spread of aquatic viruses.We firstly analyzed the intestinal microbiota of CyHV-2 infected and healthy common carp(Cyprinus carpio)from a aquaculture pond with CyHV-2 pandemic,and observed significant difference in the richness of Enterobacteriaceae and Pseudomonas between CyHV-2 infected and healthy carp,but no significant difference in the overall microbial structure.Furthermore,we analyzed the intestinal microbiota of two crucian carp(Carassius auratus gibelio)lines with different resistance against CyHV-2,and observed that the microbiota structure of the two crucian carp lines is highly similar,with significant difference in a few low-abundance genuses..To further investigate the potential influence of intestinal microbiota on virus infection in fish,we established a virus infection model in adult zebrafish by simulating the natural infection process of spring viremia of carp virus(SVCV)under laboratory conditions.Three-month-old zebrafish was infected with of 10~8copies SVCV by intraperitoneal injection.After the onset of the disease,they were co-reared with healthy one-month-old zebrafish.After 7 days,we selected the co-reared zebrafish with high virus load and low virus load,and analyzed the intestinal microbial composition and the expression of key factors in the innate anti-viral immune pathway.The results showed that the expression of anti-viral immune-related genes Rig-I,MxB,pkz,IFN phi1 and IFN phi2 in low-virus fish was significantly higher than that in high-virus fish,indicating that the anti-viral immune response was higher in the low-virus fish compared with high-virus fish.However,there was no significant difference in the intestinal bacterial amount and abundance of key phyla and genuses of the intestinal microbiota between the low-virus and high-virus zebrafish.Finally,the germfree zebrafish virus infection model was established.The germfree zebrafish were infected with SVCV at 10~8copies/mL.Zebrafish started to die 3 days post infection and the death maximized at day 7.The mortality rate was between 40 and 70%.The model was used to investigate the effect of intestinal microbiota and several representative commensal strains on SVCV infection in zebrafish.The results showed that the infection model was stable and reliable.No significant influence of intestinal microbiota and the commensal strains on virus infection was observed in the 24-hour interaction frame.Significant eduction in mortality of Cetobacterium and Plesimonas shigelloides on virus infection was observed in the 72-hour interaction frame.In this study,we observed no significant difference in the structure of intestinal microbiota between common carp and crucian carp with differential sensitivity to CyHV-2.Further,we established virus infection model in both adult zebrafish and germ-free zebrafish,which may promote future study in the influence of intestinal microbiota on virus infection in fish and provide a platform to selectanti-virus probitic strains.