Alterations of the Mucosal Immune Response and Microbial Community of the Skin upon Viral Infection in Rainbow Trout (Oncorhynchus mykiss)

Abstract

The skin is the largest organ on the surface of vertebrates, which not only acts as the first line of defense against pathogens but also harbors diverse symbiotic microorganisms. The complex interaction between skin immunity, pathogens, and commensal bacteria has been extensively studied in mammals. However, little is known regarding the effects of viral infection on the skin immune response and microbial composition in teleost fish. In this study, we exposed rainbow trout (Oncorhynchus mykiss) to infectious hematopoietic necrosis virus (IHNV) by immersion infection. Through pathogen load detection and pathological evaluation, we confirmed that IHNV successfully invaded the rainbow trout, causing severe damage to the epidermis of the skin. qPCR analyses revealed that IHNV invasion significantly upregulated antiviral genes and elicited strong innate immune responses. Transcriptome analyses indicated that IHNV challenge induced strong antiviral responses mediated by pattern recognition receptor (PRR) signaling pathways in the early stage of the infection (4 days post-infection (dpi)), and an extremely strong antibacterial immune response occurred at 14 dpi. Our 16S rRNA sequencing results indicated that the skin microbial community of IHNV-infected fish was significantly richer and more diverse. Particularly, the infected fish exhibited a decrease in Proteobacteria accompanied by an increase in Actinobacteria. Furthermore, IHNV invasion favored the colonization of opportunistic pathogens such as Rhodococcus and Vibrio on the skin, especially in the later stage of infection, leading to dysbiosis. Our findings suggest that IHNV invasion is associated with skin microbiota dysbiosis and could thus lead to secondary bacterial infection.

The Pathogen Aeromonas salmonicida achromogenes Induces Fast Immune and Microbiota Modifications in Rainbow Trout

“…However, the relative abundance drastically dropped 72 h after infection. In a recent study, Zhan et al showed that rainbow trout infected by infectious hematopoietic necrosis virus also exhibited a decrease in Proteobacteria accompanied by an increase in Actinobacteria [ 44 ].…”

“…These observations were reinforced by the dysbiosis ratios as half of the bacterial network was modified showing a huge effect of A. salmonicida achromogenes . It has already been shown that stress [ 16 ] or pathogen infection [ 44 , 46 ] induce multiple modifications in the relationship between bacterial populations. Understanding the dynamics within a bacterial community while the host is undergoing infection is crucial for the development of pro/pre/synbiotics in aquaculture.…”

Study on Mechanism of Lactobacillus rhamnosus Mitigating PFOA/PFOS Toxicity in Adult Zebrafish (Danio rerio)

“…Gordonia is a pathogenic bacterium capable of producing certain secondary metabolites, which cause malformation and death in seahorses [49]. Some species of Rhodococcus cause nephritis and anophthalmia in salmon [50].…”