Analysis of the Stability of a Type III Secretion System Containing Pathogenicity Island (PII-3) in the Human Pathogen Vibrio Cholerae

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University of Delaware
Vibrio cholerae is an enteric pathogen that is the causative agent of the secretory diarrhea, cholera, that affects millions of people each year. While the V. cholerae O1 serogroup pathovar strains are well studied due to their propensity to cause epidemic and pandemic cholera, a second pathovar has been identified that causes inflammatory diarrhea. Strains of this pathovar encode a Type III Secretion system (T3SS) that is present on a Pathogenicity Island (PAI), a mobile genetic element integrated into the chromosome of some non-O1 serogroup strains. Our hypothesis is that this PAI was horizontally acquired and was an essential acquisition in the emergence of this pathovar. The aims of this study were to investigate the genetic structure of T3SS island regions, examine the excision behavior of the region in strain NRT36S and reconstruct the evolutionary history of the region. To accomplish this, we first performed a bioinformatics analysis among a group of strains that contain a T3SS. We constructed a genetic deletion of cognate T3SS island integrase, intV2, and determined the excision phenotype of the island using a two stage nested PCR assay. We showed that intV2 is necessary for the excision of the region. Lastly, we performed a phylogenetic analysis of the conserved T3SS ATPase protein and associated integrases to show unique clustering patterns, indicating that this island is mosaic in structure. Additionally, phylogenetic analysis revealed the presence of two different variants of T3SSs within V. cholerae, T3SS� and T3SS�. The grouping pattern on the tree showed close relationship between the T3SS ATPase of V. cholerae NRT36S, V. parahaemolyticus, and V. mimicus suggesting that this virulence system may have been passed horizontally among these different species of bacteria in the past.
Research Subject Categories::NATURAL SCIENCES::Biology::Organism biology::Microbiology, Biological Sciences