Figure 2.

Five mechanisms for HGT. Conjugation is the HGT of bacteria by direct contact, and the DNA of the donor bacteria is transmitted to the recipient bacteria by the conjugative pili or adhesins. Transformation: the lysed bacteria (dashed line) release naked DNA fragments, which are acquired, integrated, and expressed by other bacteria. Transduction: a type of HGT mediated by bacteriophage. After the bacteriophage infects the bacteria, bacterial DNA fragments might be accidentally loaded into the bacteriophage head. The bacteriophage that carries the host bacteria’s DNA is released and infects a new bacterium to complete HGT. The bacteriophage with a red head represents that carries bacteriophage DNA and the blue head represents a bacteriophage that carries host bacterial DNA. Membrane vesicle fusion: the bacterial outer membrane bulges to form 20–250 nm MVs that carry genetic material and releases it into the environment. MVs have a lipid bilayer biological membrane that can protect and transport cargo and fuse with target cells to deliver contents. GTAs: bacteria that carry the GTA gene in chromosomes (brown fragment) can produce GTA. Most GTA particles carry a small random DNA fragment of the producing bacteria (blue particle head). A few GTA particles carry partial fragments of the GTA gene (brown particle head). Because these GTA gene fragments are not complete, they cannot be encoded into new GTA particles after being transferred into the recipient cell. GTA particles are released by bacteria cell lysis (dashed line).