Genomic characterization and pathological effects of Vibrio diabolicus in experimentally infected juvenile Seriola rivoliana.

Abstract

Bacterial pathogens of the family Vibrionaceae are widespread in aquatic environments and pose a substantial threat to economically important fish species. In this study, we isolated and characterized a Vibrio diabolicus strain using whole-genome sequencing, which yielded a 5,039,696 bp genome distributed across two chromosomes: a larger chromosome (3,108,246 bp) and a smaller one (1,931,450 bp). The genome encoded multiple multidrug resistance genes and several virulence-associated factors, including the type III secretion system chaperone VcrH on the large chromosome and thermolabile hemolysin (tlh) on the smaller chromosome. Additional genes of interest present on the larger chromosome included clpA, clpS, clpX, clpP, two putative cas3 type I genes, and TnXax1, a Tn3 family transposase. Pathogenicity was assessed through a four-day intraperitoneal infection bioassay in juvenile Seriola rivoliana using bacterial concentrations of 1.4 × 10, 2.36 × 10, and 2.1 × 10 CFU/mL. Although no mortality was recorded, infected fish presented pronounced pathological alterations, including severe hemorrhages, muscle necrosis, granulomatous inflammation, and degeneration of intestinal tissues. Marked mucosal hyperplasia and increased infiltration of macrophages and lymphocytes were also observed in the intestine. Overall, these findings provide genomic and pathological insights into a V. diabolicus strain circulating in marine aquaculture systems and highlight its potential role as an emerging opportunistic pathogen capable of causing significant sublethal tissue damage despite limited mortality.