Horizontal Gene Transfer (HGT) can be defined as a non-sexual process that enables the exchange of genetic information between genomes. Although HGT mainly occurs between prokaryotic genomes, an increasing number of examples involving eukaryotic host genomes have recently been described. <em>Agrobacterium</em> bacteria are capable of transferring and integrating DNA into the genome of eukaryotic cell hosts by the HGT mechanism. The transference of genetic material via <em>Agrobacterium</em>-mediated transformation is widely used in biotechnology to generate plants with desired genetic sequences. In the last years, it has been shown that various bacterial species including <em>Bartonella henselae</em> <em>Rhizobium etli</em> or even <em>Escherichia coli</em>, are able to genetically transform eukaryotic cells under laboratory growth conditions. The genetic phenomenon of horizontal gene transfer has evolutionary significance since it enables to bypass barriers between kingdoms in order to acquire nucleotide sequences that may eventually have some adaptive advantage. Moreover, the mechanism of horizontal transfer challenges a narrow vision of the eukaryotic genome as a fixed entity.
