- Horizontal gene transfer (HGT), also known as lateral gene transfer, is the movement of genetic material between organisms in a manner other than traditional vertical inheritance (from parent to offspring).
- Unlike vertical gene transfer, which involves the transmission of DNA during reproduction, HGT enables the direct exchange of genes between unrelated species or across taxonomic boundaries. This process has profound implications for evolution, adaptation, and the spread of traits such as antibiotic resistance, making it one of the most important drivers of genetic innovation in the microbial world.
- HGT is particularly common in prokaryotes, such as bacteria and archaea, where it plays a central role in shaping genomes. Three major mechanisms of HGT in bacteria are transformation, where cells uptake free DNA from the environment; transduction, where bacteriophages (viruses that infect bacteria) transfer DNA between hosts; and conjugation, a process involving direct cell-to-cell contact and the transfer of plasmids or other mobile genetic elements. These mechanisms allow bacteria to rapidly acquire new traits, such as metabolic pathways, virulence factors, and antibiotic resistance genes, which can spread quickly through microbial populations.
- In eukaryotes, horizontal gene transfer is less common but still significant. It has been observed in plants, fungi, protists, and even animals, often involving genes transferred from bacteria or endosymbiotic organisms. For example, some insects and nematodes have acquired bacterial genes that allow them to digest plant cell walls, while plants have integrated genes from fungi or bacteria that improve stress resistance. The origin of mitochondria and chloroplasts—key organelles in eukaryotic cells—is also attributed to ancient HGT events through endosymbiosis, where entire genomes from engulfed bacteria contributed to modern eukaryotic lineages.
- The evolutionary significance of HGT lies in its ability to accelerate adaptation and diversification. By bypassing the slow process of mutation and natural selection alone, organisms can instantly acquire complex traits that took other species millions of years to evolve. This has profound consequences for microbial ecology, allowing microbes to thrive in extreme environments, metabolize unusual substrates, and develop resistance to drugs. In pathogens, HGT is a major factor in the emergence of new infectious diseases and multidrug-resistant strains, posing serious challenges to public health.
- Modern genomics has revealed the widespread impact of HGT across the tree of life. Comparative genome studies show that many genes in both prokaryotes and eukaryotes have origins traceable to distant lineages, challenging the traditional view of evolution as strictly branching and linear. Instead, life’s history is increasingly seen as a web of genetic exchange, where vertical inheritance is complemented by lateral connections that blur species boundaries.
- Beyond natural processes, horizontal gene transfer has become a tool in biotechnology and genetic engineering. Scientists exploit HGT-like mechanisms to insert beneficial genes into crops, microbes, or animals, creating genetically modified organisms (GMOs) with improved traits such as pest resistance, enhanced nutrition, or bioremediation capacity. Understanding HGT also informs strategies to mitigate risks, such as preventing the unintended spread of engineered genes to wild populations.
