Genomic islands in pathogenic and environmental microorganisms

Horizontal gene transfer is an important mechanism for the evolution of microbial genomes. Pathogenicity islands - mobile genetic elements that contribute to rapid changes in virulence potential - are known to have contributed to genome evolution by horizontal gene transfer in many bacterial pathogens. Increasing evidence indicates that equivalent elements in nonpathogenic species - genomic islands - are important in the evolution of these bacteria, influencing traits such as antibiotic resistance, symbiosis and fitness, and adaptation in general. This review discusses the recent lessons that have been learned from pathogenicity islands in pathogenic microorganisms and how they apply to the role of genomic islands in commensal, symbiotic and environmental bacteria.