Integrated analysis of intestinal microbiota and metabolomic reveals that decapod iridescent virus 1 (DIV1) infection induces secondary bacterial infection and metabolic reprogramming in Marsupenaeus japonicus.

In recent years, with global warming and increasing marine pollution, some novel marine viruses have become widespread in the aquaculture industry, causing huge losses to the aquaculture industry. Decapod iridescent virus 1 (DIV1) is one of the newly discovered marine viruses that has been reported to be detected in a variety of farmed crustacean and wild populations. Several previous studies have found that DIV1 can induce Warburg effect-related gene expression. In this study, the effects of DIV1 infection on intestinal health of shrimp were further explored from the aspects of histological, enzymatic activities, microorganisms and metabolites using Marsupenaeus japonicus as the object of study. The results showed that obvious injury in the intestinal mucosa was observed after DIV1 infection, the oxidative and antioxidant capacity of the shrimp intestine was unbalanced, the activity of lysozyme was decreased, and the activities of digestive enzymes were disordered, and secondary bacterial infection was caused. Furthermore, the increased abundance of harmful bacteria, such as Photobacterium and Vibrio, may synergized with DIV1 to promote the Warburg effect and induce metabolic reprogramming, thereby providing material and energy for DIV1 replication. This study is the first to report the changes of intestinal microbiota and metabolites of M. japonicus under DIV1 infection, demonstrating that DIV1 can induce secondary bacterial infection and metabolic reprogramming. Several bacteria and metabolites highly associated with DIV1 infection were screened, which may be leveraged for diagnosis of pathogenic infections or incorporated as exogenous metabolites to enhance immune response.

Host-microbiota interactions and responses of Metapenaeus ensis infected with decapod iridescent virus 1.

Introduction: Decapod iridescent virus 1 (DIV1) has caused severe economic losses in shrimp aquaculture. So far, Researchs on DIV1-infected shrimp have mainly focused on the hemocytes immune response, while studies on the host-intestine microbiota interactions during DIV1 infection have been scarce. Methods: This study determined the lethal concentration 50 (LC50) of DIV1 to Metapenaeus ensis, preliminarily determining that M. ensis could serve as a susceptible object for DIV1. The interactions and responses between the immune and intestine microbiota of shrimp under DIV1 infection were also investigated. Results and Discussion: DIV1 infection decreases intestine bacterial diversity and alters the composition of intestine microbiota. Specifically, DIV1 infection decreases the abundance of potentially beneficial bacteria (Bacteroidetes, Firmicutes, and Actinobacteria), and significantly increases the abundance of pathogenic bacteria such as Vibrio and Photobacterium, thereby increasing the risk of secondary bacterial infections. The results of PICRUSt functional prediction showed that altered intestine microbiota induces host metabolism disorders, which could be attributed to the bioenergetic and biosynthetic requirements for DIV1 replication in shrimp. The comparative transcriptomic analysis showed that some metabolic pathways related to host immunity were significantly activated following DIV1 infection, including ncRNA processing and metabolic process, Ascorbate and aldarate metabolism, and Arachidonic acid metabolism. M. ensis may against DIV1 infection by enhancing the expression of some immune-related genes, such as Wnt16, heat shock protein 90 (Hsp90) and C-type lectin 3 (Ctl3). Notably, correlation analysis of intestinal microbial variation with host immunity showed that expansion of pathogenic bacteria (Vibrio and Photobacterium) in DIV1 infection could increased the expression of NF-κB inhibitors cactus-like and Toll interacting protein (Tollip), which may limit the TLR-mediated immune response and ultimately lead to further DIV1 infection. Significance and Impact of the Study: This study enhances our understanding of the interactions between shrimp immunity and intestinal microbiota. The ultimate goal is to develop novel immune enhancers for shrimp and formulate a safe and effective DIV1 defense strategy.

The Molecular Mechanism of Hemocyte Immune Response in Marsupenaeus japonicus Infected With Decapod Iridescent Virus 1.

As a new type of shrimp lethal virus, decapod iridescent virus 1 (DIV1) has caused huge economic losses to shrimp farmers in China. Up to now, DIV1 has been detected in a variety of shrimps, but there is no report in Marsupenaeus japonicus. In the current study, we calculated the LC50 to evaluate the toxicity of DIV1 to M. japonicus and determined through nested PCR that M. japonicus can be the host of DIV1. Through enzyme activity study, it was found that DIV1 can inhibit the activities of superoxide dismutase, catalase, lysozyme, and phenoloxidase, which could be a way for DIV1 to achieve immune evasion. In a comprehensive study on the transcriptomic changes of M. japonicus in response to DIV1 infection, a total of 52,287 unigenes were de novo assembled, and 20,342 SSR markers associated with these unigenes were obtained. Through a comparative transcriptomic analysis, 6,900 differentially expressed genes were identified, including 3,882 upregulated genes and 3,018 downregulated genes. The Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that some GO terms related to virus invasion, replication, and host antiviral infection were promoted under DIV1 infection, such as carbohydrate binding, chitin binding, chitin metabolic process, and DNA replication initiation, and some KEGG pathways related to immune response were significantly influenced by DIV1 infection, including Toll and IMD signaling pathway, JAK-STAT signaling pathway, IL-17 signaling pathway, C-type lectin receptor signaling pathway, complement and coagulation cascades, antigen processing and presentation, necroptosis, apoptosis, NOD-like receptor signaling pathway, apoptosis-multiple species, and TNF signaling pathway. Further analysis showed that STAT, Dorsal, Relish, heat shock protein 70 (HSP70), C-type lectins, and caspase play an important role in DIV1 infection. This is the first detailed study of DIV1 infection in M. japonicus, which initially reveals the molecular mechanism of DIV1 infection in M. japonicus by using the transcriptome analysis of hemocytes combined with enzyme activity study.