Vibrio vulnificus and blood cells interaction: a dualRNAseq approach uncovers a fatal retrotransposon storm induced by a toxin of the MARTX family
Résumé
Introduction: Vibrio vulnificus is a marine and zoonotic bacterial species linked to climate change. The species is divided into five lineages related to human vibriosis and one pathovar associated with fish vibriosis. This pathovar encompass the V. vulnificus strains that belong to a zoonotic clonal-complex, which can cause lethal septicemia through ingestion or contact. This septicaemia, also known as vibriosis, shows very similar clinical signs in humans and fish, with the eel being the most susceptible host. In previous studies we have shown that the RtxA1 toxin, the main virulence factor of the species, is associated with an early cytokine storm in the blood that ends with the death of the infected individual in 24-48 hours, irrespective of the host. Objective: To perform a comprehensive study of the complex host-pathogen interaction that occurs in the blood during septicemia using eel vibriosis as a model, and to better understand the role of the RtxA1 toxin in that interaction. Method: We designed an ex vivo approach to perform dualRNAseq and analyze in parallel the host and bacterial transcriptomes during early vibriosis. We incubated a representative strain of the V. vulnificus zoonotic clonal-complex (parental and mutant strain defective in RtxA1) in eel plasma containing erythrocytes or leukocytes for 3 hours to simulate early vibriosis in blood. After that time, we harvested the RNA and analyzed the bacterial and eel transcriptome. The transcriptomic results that were detected as relevant were confirmed by using bacterial mutants in certain genes and performing a series of phenotypic in vivo, ex vivo and in vitro experiments specifically designed for each gene or cellular process. Findings: The results obtained in this work show that in contact with blood cells, V. vulnificus expresses a broad arsenal of defense (LPS-modification and nutritional immunity) and attack systems (prominently the RtxA1 toxin, but also its major hemolysin (VvhA) and the VgrG toxin (part of type VI secretion system [T6SS]. In response, blood cells activate their own defense systems (RBCs activate degranulation, while WBCs activate NO and ROS production). In addition, both cell types show signs of bacterial attack, manifested as the activation of cell death, inflammation markers that correspond to the early stages of a cytokine storm. Finally, we revealed the activation of a potential retrotransposon storm in WBCs, which could underlie the RNA-based immune response previously observed in vivo. This storm is specifically associated with RtxA1 and we propose that it is involved in the dysregulated immune response triggered by this pathogen, the main cause of the death of the host. Conclusion: This study provides critical insights into the complex host-pathogen interactions during early vibriosis, using eel plasma as a model. Our results deepen our understanding of the molecular interplay underlying septicemia and underscore the importance of RtxA1 in shaping the outcome of the disease. Our results also offer showcase a potential avenue for future therapeutic interventions against animal and human vibriosis.