Fast rates of evolution in bacteria due to horizontal gene transfer

Horizontal gene transfer is recognized as a major force in shaping bacterial gene content and has gained incredible attention over the last decade, in part due to the fast growing number of sequenced bacterial genomes. The genomic data have permitted an appreciation that rapid evolution in bacteria is mainly the result of the ability of almost all bacteria to horizontally acquire genes over evolutionary time. Many of these horizontal transfers can occur with multiple genes transferred per event. This chapter discusses some of the features and patterns of rapid evolution via horizontal transfer. In particular, it notes that methods which estimate rates of gene transfers, such as via parsimony or via maximum likelihood, suggest that the estimated levels of horizontal transfer are smaller than the true rates.