FIGURE 1.

The phylogeny of V. cholerae and history of cholera. The maximum likelihood phylogenetic tree was constructed from a concatenated alignment of locally collinear blocks (2,602,418 bp) and using the GTR gamma substitution model with 100 bootstrap replicates (indicated on tree nodes). Non-O1 RC385 (O135) serves as the outgroup. The scale bar represents nucleotide substitutions per site. The geographical source and year of isolation are indicated next to the strain names. The gray boxes and dots indicate serogroup replacement by the ancestor of some strains of the phylocore genome (PG) group. The timeline shows significant events in the history of cholera, and their inferred positions in the phylogenetic tree are indicated by their corresponding color. 6P and 7P denote strains of the sixth and seventh pandemic, respectively.