Importation of the major pilin TcpA gene and frequent recombination drive the divergence of theVibriopathogenicity island inVibrio cholerae

Abstract

The Vibrio pathogenicity island (VPI) encodes the toxin-coregulated pilus and other virulence factors for Vibrio cholerae to colonize the human intestine to cause cholera. We assessed the level of genetic variation of VPI in nine nonpandemic isolates, and compared them with the sixth and seventh pandemic strains by sequencing c. 5 kb each from the start, middle and end regions of the VPI. Variation is similar among the three regions at around 2%, except for the tcpA gene, which has a much higher level of variation (23%). Numerous recombination segments were identified with sizes up to 2177 bp. Nearly all VPI genes sequenced have a ratio of synonymous to nonsynonymous substitutions considerably lower than that for housekeeping genes, suggesting that VPI genes are under positive selection pressure for change. The tagA gene was deleted or damaged in six isolates, which is likely to affect the efficiency of colonization of the human intestine. Two genes, orf2 and acfD, previously found to be translated differently in the sixth and seventh pandemic strains, were determined to be mutant in the seventh and sixth pandemic strains, respectively. These findings enhance our understanding of variation in the VPI, and of the pathogenic potential of VPI-positive environmental isolates.

Characterization of pathogenicity island prophage in clinical and environmental strains of Vibrio cholerae

“…The findings reported here are supported by those of Karaolis et al (2001) who demonstrated that the central region of the VPI of tcpA contains most of the divergence between the VPIs of the 6th (classic) and the 7th (El Tor) pandemic strains. Previous studies by others have described that the genetic variants of the TCP island were carried by a number of environmental V. cholerae strains belonging to non-epidemic serogroups (Boyd & Waldor, 2002;Mukhopadhyay et al, 2001;Tay et al, 2008). Overall, the consensus all published reports have indicates mutational events in the tcp region.…”

Molecular analysis of non-O1/non-O139 Vibrio choleraeisolated from hospitalised patients in China

“…PCR assays (Table 2) were used for the detection of the ctxAB [39], tcpA [40], zot [41], NAG-ST [16], T3SS ( vcsC2 and vcsV2 ) [16,28], ompW [42], toxR [42] and hlyA genes [43]. All isolates were positive for V. cholerae specific gene ompW by PCR, but were negative for ctxAB , zot , tcpA and NAG-ST. All isolates were positive for toxR (Table 1), except for N743 which was toxR negative.…”

Type IV Pilin Proteins: Versatile Molecular Modules

“…The O1 serogroup contains the genetically similar classical and El Tor biotypes, which vary at only a few loci, including that for the major pilin subunit, TcpA (387). Comparison of TcpA sequences between those two serogroups showed that they were ϳ80% identical, with the N terminus being the most highly conserved region.…”

“…Comparison of TcpA sequences between those two serogroups showed that they were ϳ80% identical, with the N terminus being the most highly conserved region. The primary mechanism responsible for generating TcpA diversity was proposed to be recombination rather than mutation (387). Even small sequence changes in TcpA have profound effects on pilus function, as single point mutations in the D region caused a loss of pilus bundling, a phenotype important to pathogenesis.…”