Horizontal Gene Transfer and Microevolution in Soil

High-throughput methods for DNA sequencing have cataloged the composition of thousands of bacterial genomes, including those of many soil bacteria. Regardless of the impact of ecological factors on bacterial microevolution, whole-genome sequencing and comparative genome analysis do provide strong and compelling evidence for the importance of horizontal gene transfer (HGT) in the general evolution of bacteria, including a range of typical soil bacteria. In particular sites in soil, such as the rhizosphere and mycosphere, HGT is well known to promote the exchange of genetic material. Horizontal transfer of chromosomal DNA enables bacteria to access the genetic diversity present in other members of its own population or in separately evolving organisms. The chapter examines the significance of HGT as an adaptive mechanism that can genetically shape soil bacterial communities, and attemts to recommend strategies for future research. Natural transformation is the physiologically regulated uptake of extracellular DNA into transformation-competent bacteria, that is, bacteria that have reached the state of natural competence.