Sequencing of more than 1,600 microbial genomes has been complete, and rigorous studies are underway to reveal the mechanisms of evolution which gave rise to the great variety in combination of gene functions encoded on these genomes. Although comparative genomics based on orthologous genes has elucidated a great deal of the phylogenetic relationship among the sequenced genomes, the mechanisms which have shaped the current states of the microbial genomes remain elusive. Particularly, contribution of external forces such as horizontal gene transfer and pressure from environmental factors to genome evolution has yet to be investigated. This special issue is intended to spur efforts to elucidate mechanisms of evolutionary forces acting on microbial genomes. We invite investigators to contribute both research and review articles focusing on the evolutionary mechanisms of microbial genomes to this special issue. Both experimental and computational works, or their hybrid, will be considered. We are particularly interested in articles attempting novel approaches in comparative genomics. Potential topics include, but are not limited to:

• Horizontal gene transfer between phylogenetically distant organisms
• Orthologous gene comparison versus gene content comparison
• Environmental factors and gene contents
• Evolution of chromosomes and plasmids
• Mobile genetic elements and genomes
• Comparative studies of microbial epigenetic systems

Before submission authors should carefully read over the journal's Author Guidelines, which are located at http://www.hindawi.com/journals/ijeb/guidelines/. Prospective authors should submit an electronic copy of their complete manuscript through the journal Manuscript Tracking System at http://mts.hindawi.com/ according to the following timetable: