Multi-Organ Transcriptome Response of Lumpfish (Cyclopterus lumpus) to Aeromonas salmonicida Subspecies salmonicida Systemic Infection

Abstract

Lumpfish is utilized as a cleaner fish to biocontrol sealice infestations in Atlantic salmon farms. <i>Aeromonas salmonicida</i>, a Gram-negative facultative intracellular pathogen, is the causative agent of furunculosis in several fish species, including lumpfish. In this study, lumpfish were intraperitoneally injected with different doses of <i>A. salmonicida</i> to calculate the LD₅₀. Samples of blood, head-kidney, spleen, and liver were collected at different time points to determine the infection kinetics. We determined that <i>A. salmonicida</i> LD₅₀ is 10² CFU per dose. We found that the lumpfish head-kidney is the primary target organ of <i>A. salmonicida</i>. Triplicate biological samples were collected from head-kidney, spleen, and liver pre-infection and at 3- and 10-days post-infection for RNA-sequencing. The reference genome-guided transcriptome assembly resulted in 6246 differentially expressed genes. The <i>de novo</i> assembly resulted in 403,204 transcripts, which added 1307 novel genes not identified by the reference genome-guided transcriptome. Differential gene expression and gene ontology enrichment analyses suggested that <i>A. salmonicida</i> induces lethal infection in lumpfish by uncontrolled and detrimental blood coagulation, complement activation, inflammation, DNA damage, suppression of the adaptive immune system, and prevention of cytoskeleton formation.