The O1 serogroup is further divided into classical and El Tor biotypes on the basis of their biochemical properties and phage susceptibilities ( 18, 27). cholerae that have epidemic and pandemic potential belong to serogroups O1 and O139. cholerae strains are classified using the lipopolysaccharide O antigen, which identifies over 200 serogroups. The pathogen is endemic to coastlines and estuarine ecosystems around the world but can spread worldwide, causing pandemics ( 18, 35). It is estimated that the disease causes the deaths of 120,000 people worldwide every year and infects many more, mostly children between 1 and 5 years old ( 18, 27). Vibrio cholerae is the causative agent of Asiatic cholera. Thus, VieA is a major regulator of genes in the classical biotype under virulence gene-inducing conditions. A large fraction (20.8%) of the genes that are differentially expressed in the classical versus the El Tor biotype are controlled by VieA in the classical biotype. In contrast, only five genes were regulated by VieA in the El Tor biotype. VieA predominantly regulates gene expression in the classical biotype 401 genes (10.3% of the genome), including those encoding proteins required for virulence, exopolysaccharide biosynthesis, and flagellum production as well as those regulated by σ E, are differentially expressed in the classical vieA deletion mutant. We determined the VieA regulon in both biotypes by transcriptome comparison of wild-type and vieA deletion mutant strains.
In addition, the vieSAB genes, which were originally identified as regulators of ctxA transcription, were expressed at a fivefold higher level in the classical biotype. The expression of genes encoding virulence factors was higher in the classical than in the El Tor biotype. These gene expression differences may contribute to the enhanced survival capacity of the El Tor biotype in environmental reservoirs. The expression of genes encoding proteins required for biofilm formation, chemotaxis, and transport of amino acids, peptides, and iron was higher in the El Tor biotype.
A total of 524 genes (13.5% of the genome) were found to be differentially expressed in the two biotypes. Differences in whole-genome expression patterns between the classical and El Tor biotypes of Vibrio cholerae O1 were determined under conditions that induce virulence gene expression in the classical biotype.
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