In silico comparative study of the genomic islands of Vibrio cholerae MJ1236 with those of Classical and El Tor N16961 strains of Vibrio cholerae

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 (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 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.