Differences in gene expression between the classical and El Tor biotypes of Vibrio cholerae O1

Abstract

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. A total of 524 genes (13.5% of the genome) were found to be differentially expressed in the two biotypes. 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. These gene expression differences may contribute to the enhanced survival capacity of the El Tor biotype in environmental reservoirs. The expression of genes encoding virulence factors was higher in the classical than in the El Tor biotype. 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. We determined the VieA regulon in both biotypes by transcriptome comparison of wild-type and vieA deletion mutant strains. 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 sigmaE, are differentially expressed in the classical vieA deletion mutant. In contrast, only five genes were regulated by VieA in the El Tor biotype. 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. Thus, VieA is a major regulator of genes in the classical biotype under virulence gene-inducing conditions.

FIG. 1.

Functional categories of the differentially expressed genes in V. cholerae biotypes. The number of genes whose expression is increased in classical or El Tor biotype is presented according to the functions assigned by TIGR genome database.

FIG. 2.

Chromosomal mapping of the differentially expressed genes between the classical and El Tor biotypes. Differentially regulated genes are presented in genome order. The magnitude of expression is given with a color-coded scale (red, high in classical biotype; green, high in El Tor biotype; yellow, equally expressed in both biotypes). The expression profiles of selected gene clusters, (A) tcp, (B) ctx, (C) vie, (D) peptide ABC transporter, (E) msh, (F) vibriobactin biosynthesis, (G) vps region, (H) chemotaxis, (I) amino acid ABC transporter, (J) iron transport, and (K) chemotaxis, are shown.

FIG. 3.

Functional categories of the differentially expressed genes between C-wt and C-ΔvieA. The number of genes whose expression is increased or decreased in C-ΔvieA in comparison to the classical strain is presented according to the functions assigned by TIGR genome database.

FIG. 4.

Heat maps of differentially expressed genes between C-wt and C-ΔvieA. The magnitude of expression is given with a color-coded scale (red, induced; green, repressed). The expression profiles of selected gene clusters, (A) vps, (B) eps, (C) genes located in VPI, (D) genes involved in chemotaxis and motility, (E) vieSAB, and (F) rseABC and rpoE, are shown.

FIG. 5.

(A) Motility phenotypes of E-wt, C-wt, E-ΔvieA, and C-ΔvieA on LB soft agar plates. (B) Bar graphs showing the diameters of the motility zones of E-wt, C-wt, E-ΔvieA, and C-ΔvieA after 20 h of incubation at 30°C.