Figure 1.

The many routes for horizontal gene transfer. DNA can be transferred between individuals by multiple mechanisms falling broadly into three categories. In transduction (blue text), DNA is transferred either as part of the phage genome itself or as additional DNA packaged into phage particles or gene transfer agents. In conjugation (yellow text), donor cells form conjugative pili, typically encoded on plasmids or integrative conjugative elements, through which DNA is transferred. Finally, transformation (red text) is the process by which DNA in the environment is actively taken up by the donor cell. In addition, recent studies have shown that bacteria can also transfer DNA fragments in membrane-bound vesicles and via nanotubes.