Genome plasticity in Enterobacteriaceae

The comparative analysis of multiple representatives of the genomes of part icular species are leading us away from a view of bacterial genomes as stat ic, monolithic structures towards the view that they are relatively variabl e, fluid structures. This plasticity is mainly the result of the rearrangem ent of genes within the genome and the acquisition of novel genes by horizo ntal transfer systems, e.g. plasmids, bacteriophages, transposons or gene c assettes. These mechanisms often act in concert thus generating a complex g enetic structure. Genomic variations are not a phenomenon at the DNA level alone, they influence the phenotype of a bacterium as well and can render a formerly harmless organism into a hazardous pathogen. This review deals no t only with the mechanisms of genome rearrangements and the horizontal tran sfer of genes in Enterobacteriaceae but also points out that mobile genetic elements themselves are subjected to variation.