Analysis of the Stability of a Type III Secretion System Containing Pathogenicity Island in the Human Pathogen Vibrio cholerae

Abstract

Vibrio cholerae is an enteric pathogen that is the causative agent of the secretory diarrhea, cholera, that affects millions each year. While the O1 serogroup V. cholerae strains are the most well studied due to their propensity to cause epidemic and pandemic cholera, a second pathovar has been identified that causes inflammatory diarrhea (Shin et al., 2011). These strains encode a Type III Secretion system (T3SS). This system is present on a Pathogenicity Island (PAI), a mobile genetic element integrated into the chromosome of some non-O1 serogroup strains (Dziejman et al., 2005). The aim of this research was to examine the genetic make-up of T3SS island regions and understand the excision behavior of the region in strain NRT36S (Chen et al., 2007). We constructed a deletion of the cognate island integrase, intV2, and determined the excision phenotype of the island using a two stage nested PCR assay. The results of this assay showed that intV2 is necessary for the excision of the region. Another aim of this work was to examine the evolutionary history of this island region amongst Vibrio and other species of bacteria. A phylogenetic analysis of the conserved T3SS ATPase protein showed the presence of two different variants of T3SSs within V. cholerae, T3SSα and T3SSα. Additionally, the grouping pattern on the tree showed the close relationship between the T3SS ATPase of V. cholerae NRT36S, V. parahaemolyticus, and V. mimicus suggesting that this virulence system was passed horizontally among these different species of bacteria in the past (Morita et al., 2013).