The evolution of the Vibrio genome: the discovery of the pan-genome and the functional specialization of chromosomes.

The genus Vibrio comprises a taxonomically and functionally diverse group of bacteria, including numerous species of relevance to human health, marine ecosystems, and aquaculture. In this study, we performed a comparative pan-genome and core-genome analysis of 76 reference Vibrio genomes to investigate genomic diversity, chromosome-specific functional organization, and virulence-associated gene content across the genus. The pan-genome of the genus has an open structure, while the size of the core-genome remains stable and is significantly smaller than the proportion of added genes. The total number of genes per species varies from 2,765 to 5,693. Functional annotations by COG categories revealed differences in profiles between chromosomes. Additionally, a search for virulence factors was performed using the VFDB database, with the highest number found in the pathogenic species V. cholerae and V. parahaemolyticus. Taken together, our results demonstrate extensive genomic diversity within the genus Vibrio and indicate chromosome-specific functional specialization, with accessory genome components-particularly on the second chromosome-being closely associated with pathogenic potential. These findings contribute to a deeper understanding of genome organization, ecological adaptation, and virulence evolution in vibrios and provide a basis for future comparative and functional genomic studies relevant to public health and aquaculture.