Insights into American lobster (Homarus americanus) defence mechanisms against Vibrio splendidus

Members of the Vibrio genus are widespread, Gram-negative, facultatively anaerobic, heterotrophic bacteria that inhabit many aquatic environments and contribute to nutrient cycling. They display different lifestyles, living freely in the water column, residing in sediments, or forming associations with other organisms, including as constituents of the crustacean gut microbiota. While some Vibrio species form mutualistic symbioses, others act as pathogens, causing vibriosis and significant mortality in marine fish and/or shellfish populations. In this study, the American lobster (Homarus americanus) was able to defend itself against Vibrio splendidus, with no mortality observed during the challenge. We performed RNA-Seq analysis of the hepatopancreatic tissue, an important immune organ in crustaceans, to elucidate the molecular mechanisms of this defence response. The expression of over 21,000 genes was measured, where 1250 were identified as differentially expressed. Seventy-two of these differentially expressed genes were annotated as having a role related to host immune or stress response. Of particular significance is the differential expression of several anti-lipopolysaccharide factors (ALFs), pentraxin serum amyloid A-5 protein-like (SAA-5-like), crustacean hyperglycemic hormone (CHH) genes, and other genes involved in signalling pathways, coagulation, and antioxidant defence systems. The distinct regulation of individual ALF and lectin genes may suggest a tailored immune response to V. splendidus. These findings provide novel insights into the molecular mechanisms regulating immune responses in the American lobster and contribute to our broader understanding of host-pathogen interactions in marine crustaceans.