The complete genomic sequence of Vibrio cholerae El Tor N16961, a Gram-negative gamma-Proteobacterium, was determined to be 4,033,460 base pairs, consisting of two circular chromosomes of 2,961,146 bp and 1,072,314 bp. These chromosomes encode 3,885 open reading frames (ORFs), with the majority of essential genes for cell functions and pathogenicity located on the large chromosome. The small chromosome contains a higher proportion of hypothetical genes and genes of unknown function, as well as a gene capture system (integron island) and host addiction genes typically found on plasmids, suggesting it may have originated as a megaplasmid captured by an ancestral Vibrio species. The genome analysis revealed that the two chromosomes have distinct gene distributions, with the large chromosome containing genes essential for growth and virulence, while the small chromosome has a higher proportion of hypothetical genes. The small chromosome also carries genes involved in horizontal gene transfer, indicating its role in the evolution of pathogenicity. Comparative genomics showed that the two chromosomes have different gene contents, with the large chromosome containing more genes related to essential functions, while the small chromosome has a higher proportion of genes with unknown functions. The Vibrio cholerae genome provides insights into how a free-living environmental organism evolved into a significant human pathogen through horizontal gene transfer. The genome sequence also reveals the presence of various virulence factors, including toxins, surface antigens, and adhesins, as well as genes involved in colonization and pathogenicity. The genome analysis highlights the importance of gene transfer in the emergence and evolution of bacterial pathogens, and provides a foundation for understanding the molecular mechanisms underlying the pathogenicity of Vibrio cholerae. The study also identifies the role of the small chromosome in the evolution of Vibrio species, suggesting that it may have been acquired from other bacterial species and integrated into the Vibrio genome. The genome sequence of Vibrio cholerae is a valuable resource for understanding the molecular basis of its pathogenicity and for studying the evolution of bacterial pathogens.The complete genomic sequence of Vibrio cholerae El Tor N16961, a Gram-negative gamma-Proteobacterium, was determined to be 4,033,460 base pairs, consisting of two circular chromosomes of 2,961,146 bp and 1,072,314 bp. These chromosomes encode 3,885 open reading frames (ORFs), with the majority of essential genes for cell functions and pathogenicity located on the large chromosome. The small chromosome contains a higher proportion of hypothetical genes and genes of unknown function, as well as a gene capture system (integron island) and host addiction genes typically found on plasmids, suggesting it may have originated as a megaplasmid captured by an ancestral Vibrio species. The genome analysis revealed that the two chromosomes have distinct gene distributions, with the large chromosome containing genes essential for growth and virulence, while the small chromosome has a higher proportion of hypothetical genes. The small chromosome also carries genes involved in horizontal gene transfer, indicating its role in the evolution of pathogenicity. Comparative genomics showed that the two chromosomes have different gene contents, with the large chromosome containing more genes related to essential functions, while the small chromosome has a higher proportion of genes with unknown functions. The Vibrio cholerae genome provides insights into how a free-living environmental organism evolved into a significant human pathogen through horizontal gene transfer. The genome sequence also reveals the presence of various virulence factors, including toxins, surface antigens, and adhesins, as well as genes involved in colonization and pathogenicity. The genome analysis highlights the importance of gene transfer in the emergence and evolution of bacterial pathogens, and provides a foundation for understanding the molecular mechanisms underlying the pathogenicity of Vibrio cholerae. The study also identifies the role of the small chromosome in the evolution of Vibrio species, suggesting that it may have been acquired from other bacterial species and integrated into the Vibrio genome. The genome sequence of Vibrio cholerae is a valuable resource for understanding the molecular basis of its pathogenicity and for studying the evolution of bacterial pathogens.