Horizontal gene transfer and adaptive evolution in bacteria

Horizontal gene transfer (HGT) is arguably the most conspicuous feature of bacterial evolution. Evidence for HGT is found in most bacterial genomes. Although HGT can considerably alter bacterial genomes, not all transfer events may be biologically significant and may instead represent the outcome of an incessant evolutionary process that only occasionally has a beneficial purpose. When adaptive transfers occur, HGT and positive selection may result in specific, detectable signatures in genomes, such as gene-specific sweeps or increased transfer rates for genes that are ecologically relevant. In this Review, we first discuss the various mechanisms whereby HGT occurs, how the genetic signatures shape patterns of genomic variation and the distinct bioinformatic algorithms developed to detect these patterns. We then discuss the evolutionary theory behind HGT and positive selection in bacteria, and discuss the approaches developed over the past decade to detect transferred DNA that may be involved in adaptation to new environments. Bacterial DNA transfers between cells in numerous ways and becomes integrated into the genome, with diverse consequences for bacterial genomes. In this Review, Arnold, Huang and Hanage discuss the underlying theory used to infer the selective forces acting on transferred DNA and how they shape patterns of genomic variation.

Automated summary

Horizontal gene transfer is a significant feature of bacterial evolution, with the potential to alter genomes but not all events may be biologically significant. Adaptive transfers can result in detectable signatures in genomes and increased transfer rates for genes with ecological relevance.