“The evolution of microbial genomes is greatly influenced by horizontal gene transfer (HGT), where large blocks of horizontally acquired foreign sequences, often encoding virulence determinants, occur in chromosomes of pathogenic bacteria. A program design-island developed in our laboratory was used on three completely sequenced Vibrio cholerae genomes,
V. cholerae Classical O395, El Tor N16961 and MJ1236, in order to identify the putative horizontally acquired regions. The putative genomic islands check details (GIs) were graphically represented and analyzed. The study identified distinct regions in the GIs of V. cholerae MJ1236 which were shared either with the Classical or the El Tor strain of ABT-263 concentration V. cholerae. A cluster comprising of 38 ORFs was common to V. cholerae strains of MJ1236 and Classical O395 but absent in El Tor N16961. About 5% of the predicted GIs of V. cholerae MJ1236 were unique to itself. Among these unique ORFs, a region of mostly hypothetical genes was identified, where the ORFs were present in a large cluster. The results show that the HGT had played a significant role in the evolution and the differentiation of V. cholerae MJ1236. Vibrio cholerae, a Gram-negative bacterium, is the etiological agent of epidemic cholera,
that causes a severe and sometimes lethal diarrheal disease. Vibrio cholerae is classified into two serogroups: O1 and non-O1. So far, the toxigenic strains of serogroups O1
and O139 have been found to cause cholera epidemics. There are two biotypes of V. cholerae O1, Classical and El Tor. There have been seven major pandemics since 1817. Isolates of the sixth pandemic were of O1 classical biotype, whereas the seventh pandemic, which OSBPL9 started in 1961, is associated with El Tor biotype (Chaudhuri & Chatterjee, 2009). This indicated that a transition might have occurred, which largely replaced the V. cholerae Classical by V. cholerae El Tor as the causative organism for pandemicity between 1905 and 1961. In 1994, the new Matlab variants of V. cholerae El Tor replaced the seventh pandemic O1 El Tor strains in Asia and Africa as the predominant isolate from clinical cases of cholera (Safa et al., 2008). In V. cholerae, the two major virulence factors, cholera toxin (CT) and toxin coregulated pili (TCP), have been reported to be encoded on mobile genetic elements. The ctxAB genes, coding for A and B subunits of CT, are encoded on a filamentous bacteriophage CTXϕ. TCP, an essential colonization factor, was originally designated as part of a pathogenicity island named Vibrio pathogenicity island (VPI), but this island has more recently been proposed to be the genome of a filamentous phage, VPIϕ (Karaolis et al., 1999).