Effective control of bacterial infections remains a significant challenge in aquaculture. The marine bacterium Piscirickettsia salmonis (P. salmonis), responsible for piscirickettsiosis, causes widespread infections in various salmon species, leading to substantial mortality and economic losses. Despite efforts to genetically characterize P. salmonis, critical gaps persist in understanding its virulence factors, antimicrobial resistance genes, and single-nucleotide polymorphisms (SNPs). This study addresses these gaps through a comparative analysis of the pan-genome and core genomes of 80 P. salmonis strains from different geographical regions and genogroups. P. salmonis had an open pan-genome consisting of 14,564 genes, with a core genome of 1257 conserved genes. Eleven virulence-related genes were identified in the pan-genome, categorized into five functional groups, providing new insights into the pathogenicity of P. salmonis. Unique SNPs were detected in four key genes (gyrA, dnaK, rpoB, and ftsZ), serving as robust molecular markers for distinguishing the LF and EM genogroups. Notably, AMR genes identified in four LF strains suggest evolutionary adaptations under selective pressure. Functional annotation of the core genomes using the gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases demonstrated conserved gene clusters linked to essential intracellular survival mechanisms and bacterial pathogenicity. These findings suggest a direct association between core genome features and variations in pathogenesis and host–pathogen interactions across genogroups. Phylogenetic reconstruction further highlighted the influence of AMR genes on strain divergence. Collectively, this study enhances the genomic understanding of P. salmonis and lays the groundwork for improved diagnostic tools and targeted therapeutics to manage piscirickettsiosis in aquaculture.

Probiotics derived from an identical host′s gastrointestinal (GI) system confer superior colonization and provide greater benefits than other commercial sources. This study reports on the probiotic potentials of lactic acid bacteria (LAB) identified from the gut content of Ompok pabda through morphological, physiological, and molecular sequencing for their usefulness in aquaculture. Molecular sequencing confirmed two LAB strains affiliated with the genus Weissella; namely Weissella confusa OPL2 and Weissella cibaria OPL3. Each strain was evaluated for its capability to withstand conditions relevant to feed application and gastrointestinal survival, including fluctuations in temperature, NaCl concentration, pH, and gut bile. Both strains consistently tolerated acidic pH (pH 2–5), bile concentration up to 7.5%, elevated temperature (4°C–45°C), and salt concentration (3%–6%). In addition, the strains demonstrated strong cell‐surface properties, including higher hydrophobicity with time (68.77 ± 0.17 % to 69.36 ± 0.41 % in xylene, 65.62 ± 0.48 % to 67.73 ± 0.36 % in toluene), pronounced autoaggregation capacity (64.15 ± 0.35 % and 64.12 ± 0.53 % ), notable coaggregation rates of 52.79 ± 2.15 % and 53.05 ± 0.35 % with Bacillus aerius , and 50.11 ± 0.16 % and 49.51 ± 0.81 % with Staphylococcus epidermidis , for W. cibaria OPL3 and W. confusa OPL2, respectively. Furthermore, the strains showed marked in vitro antagonism against Aeromonas veronii OPP8 and Plesiomonas shigelloides OPP9. Safety assessment further supported their suitability as probiotics, as they were found nonhemolytic in nature, as well as susceptible to several commonly used antibiotics. Therefore, the findings indicate W. cibaria OPL3 and W. confusa OPL2 as a safe and promising probiotic candidate from O. pabda with clear probiotic potentials in the aquaculture industry.

Many amino acids remain undiscovered and have not yet been associated with specific genome sequences. Modules of ambiguous activity are proteins detected through experimental methods that have not yet been assigned specific geometric annotations. In our study, the potential regulatory properties of the unidentified peptides from Aeromonas veronii (accession no. PXV57966.1) were explored and analyzed using several computational approaches and tools. From this in silico approach, the physical properties, cell position, 3-D arrangement, interactions among proteins, and functionality insights of the amino acid have all been determined. Protein-protein interactions were analyzed using STRING software, which revealed that E2102 protein interacts strongly with the peptidyl-tRNA hydrolase. The in-silico analysis indicated that the protein is hydrophilic, with its secondary structure mainly composed of alpha (α) helices. According to the result, the protein contains Ribosome-binding ATPase YchF domain, which suggests it may bind to ribosomal subunits. In addition, Aeromonas veronii is an opportunistic pathogen capable of causing various infections in humans, including gastroenteritis, soft tissue infections, and bacteremia. Thus, the study will contribute to the creation of novel antimicrobial treatments for treating severe intestinal tract infections by enhancing our understanding of the role of the E2102 domain.