Marine finfish aquaculture is affected by diverse infectious diseases, and they commonly occur as co-infection. Some of the most frequent and prevalent Gram-negative bacterial pathogens of the finfish aquaculture include Piscirickettsia salmonis, Aeromonas salmonicida, Yersinia ruckeri, Vibrio anguillarum and Moritella viscosa. To prevent co-infections in aquaculture, polyvalent or universal vaccines would be ideal. Commercial polyvalent vaccines against some of these pathogens are based on whole inactivated microbes and their efficacy is controversial. Identification of common antigens can contribute to the development of effective universal or polyvalent vaccines. In this study, we identified common and unique antigens of P. salmonis, A. salmonicida, Y. ruckeri, V. anguillarum and M. viscosa based on a reverse vaccinology pipeline. We screened the proteome of several strains using complete available genomes and identified a total of 154 potential antigens, 74 of these identified antigens corresponded to secreted proteins, and 80 corresponded to exposed outer membrane proteins (OMPs). Further analysis revealed the outer membrane antigens TonB-dependent siderophore receptor, OMP assembly factor BamA, the LPS assembly protein LptD and secreted antigens flagellar hook assembly protein FlgD and flagellar basal body rod protein FlgG are present in all pathogens used in this study. Sequence and structural alignment of these antigens showed relatively low percentage sequence identity but good structural homology. Common domains harboring several B-cells and T-cell epitopes binding to major histocompatibility (MHC) class I and II were identified. Selected peptides were evaluated for docking with Atlantic salmon (Salmo salar) and Lumpfish MHC class II. Interaction of common peptide-MHC class II showed good in-silico binding affinities and dissociation constants between −10.3 to −6.5 kcal mol⁻¹ and 5.10 × 10⁻⁹ to 9.4 × 10⁻⁶ M. This study provided the first list of antigens that can be used for the development of polyvalent or universal vaccines against these Gram-negative bacterial pathogens affecting finfish aquaculture.

Vibrio anguillarum is the most frequent pathogen affecting fish worldwide. The only known virulent strains of V. anguillarum are serotypes O1, O2, and O3. Genetic differences between the serotypes that could shed insight on the evolution and serotype differences of this marine pathogen are unknown. Here, we fully sequenced and characterized a strain of V. anguillarum O1 (J382) isolated from winter steelhead trout (Oncorhynchus mykiss irideus) in British Columbia, Canada. Koch’s postulates using the O1 strain were replicated in naïve lumpfish (Cyclopterus lumpus) and compared to O2. Phenotypic and genotypic comparisons were conducted for serotypes O1, O2, and O3, using biochemical tests and bioinformatic tools, respectively. The genome of V. anguillarum O1 (J382) contains two chromosomes (3.13 Mb and 1.03 Mb) and two typical pJM1-like plasmids (65,573 and 76,959 bp). Furthermore, V. anguillarum O1 (J382) displayed resistance to colistin sulphate, which differs from serotype O2 and could be attributed to the presence of the ugd gene. Comparative genomic analysis, among the serotypes, showed that intra-species evolution is driven by insertion sequences, bacteriophages, and a different repertoire of putative ncRNAs. Genetic heterogeneity in the O-antigen biosynthesis gene cluster is characterized by the absence or the presence of unique genes, which could result in differences in the immune evasion mechanisms employed by the respective serotypes. This study contributes to understanding the genetic differences among V. anguillarum serovars and their evolution.

The polyvalent bacteriophage fp01, isolated from wastewater in Valparaiso, Chile, was described to have lytic activity across bacterial species, including Escherichia coli and Salmonella enterica serovars. Due to its polyvalent nature, the bacteriophage fp01 has potential applications in the biomedical, food and agricultural industries. Also, fundamental aspects of polyvalent bacteriophage biology are unknown. In this study, we sequenced and described the complete genome of the polyvalent phage fp01 (MH745368.2) using long- (MinION, Nanopore) and short-reads (MiSeq, Illumina) sequencing. The bacteriophage fp01 genome has 109,515 bp, double-stranded DNA with an average G+C content of 39%, and 158 coding sequences (CDSs). Phage fp01 has genes with high similarity to Escherichia coli, Salmonella enterica, and Shigella sp. phages. Phylogenetic analyses indicated that the phage fp01 is a new Tequintavirus fp01 specie. Receptor binding protein gp108 was identified as potentially responsible for fp01 polyvalent characteristics, which binds to conserved amino acid regions of the FhuA receptor of Enterobacteriaceae.