horizontal gene transfer
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What is horizontal gene transfer?
Horizontal gene transfer (HGT) is the transmission of DNA between different genomes, even across species, unlike vertical gene transfer from parent to offspring. HGT occurs between prokaryotes and eukaryotes and among eukaryotic organelles like the nucleus, mitochondrion, and chloroplast.
Mobile genetic elements like plasmids, transposons, and bacteriophages facilitate HGT through mechanisms such as transformation, conjugation, and transduction. In transformation, prokaryotes uptake free DNA. During conjugation, there is an exchange of genetic material during a temporary union between two cells. In transduction, a bacteriophage transmits DNA from one cell to another.
HGT plays a key role in adaptation and evolution in prokaryotes and eukaryotes.
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How is horizontal gene transfer different from normal inheritance?
Horizontal gene transfer (HGT) differs from normal inheritance (vertical gene transfer) because it involves the transmission of DNA between different genomes, even between different species. This is unlike vertical gene transfer, where genetic material is passed from parents to offspring during reproduction.
HGT is facilitated by mobile genetic elements like plasmids, transposons, and bacteriophages, which transfer DNA through mechanisms such as transformation, conjugation, and transduction. In contrast, normal inheritance relies on the direct passing of genetic information through reproduction. HGT allows for rapid adaptation and evolution by incorporating new genetic material into a recipient's genome through recombination or insertion.
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Which organisms commonly use horizontal gene transfer?
Horizontal gene transfer (HGT) is the transmission of DNA between different genomes, as opposed to vertical gene transfer from parent to offspring. HGT occurs between different species, including between prokaryotes and eukaryotes, and within eukaryotic organelles.
Mobile genetic elements like plasmids, transposons, and bacteriophages facilitate HGT through mechanisms such as transformation, conjugation, and transduction. Transformation involves prokaryotes taking up free DNA, conjugation involves genetic exchange during temporary cell union, and transduction involves bacteriophages transmitting DNA between cells.
HGT plays a key role in adaptation and evolution in prokaryotes and eukaryotes. For example, the transfer of a gene encoding a unique metabolic enzyme from Pasteurella bacteria to the protozoan parasite Trichomonas vaginalis is thought to have helped the latter adapt to animal hosts. Competent bacteria such as Haemophilus, Neisseria, Streptococcus, and Bacillus are efficient in DNA uptake during transformation.
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How does horizontal gene transfer happen between bacteria?
Horizontal gene transfer (HGT) in bacteria occurs via three main mechanisms:
* Transformation Bacteria take up free DNA fragments from their environment. To do this efficiently, they must be in a "competent" state, a capability that only some bacteria naturally possess. Others, like E. coli, can be made competent in the lab.-
Transduction A bacteriophage (virus that infects bacteria) transfers DNA from one bacterium to another. This is efficient because the bacteriophage protects the DNA from degradation and injects it directly into the recipient cell. However, it's limited by the bacteriophage's host range and the inefficiency of packaging bacterial DNA into the virus.
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Conjugation DNA is transferred via direct cell-to-cell contact, mediated by plasmids. Donor cells produce a sex pilus, which connects to a recipient cell, forming a bridge for DNA transfer. This allows for the inheritance of large gene segments and may explain bacteria with traits from different species.
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What are some examples of traits spread by horizontal gene transfer?
Horizontal gene transfer (HGT) facilitates the transmission of DNA between different genomes and allows organisms to acquire new traits. Examples of traits spread by HGT include:
- Antibiotic resistance: Bacteria can acquire genes encoding enzymes that inactivate antibiotics or that alter cell-wall proteins to inhibit drug uptake. Plasmids carrying antibiotic-resistant genes can be transferred between different bacterial species, leading to rapid development of widespread resistance.
- Metabolic enzymes: Genes encoding unique metabolic enzymes can be transferred between species, potentially facilitating adaptation to new environments. For example, a gene transfer from Pasteurella bacteria to the protozoan parasite Trichomonas vaginalis is suspected to have aided the latter's adaptation to animal hosts.
- Adaptation and survival: HGT may enable organisms to adapt and survive in specific environments. The exchange of a gene from a human cell to the bacterium Neisseria gonorrhoeae may have allowed the organism to adapt and survive in humans.
- New characteristics: Fragments of DNA from one organism can be taken up by another, allowing the recipient organism to acquire new characteristics.
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Why is horizontal gene transfer important for evolution and medicine?
Horizontal gene transfer (HGT) is crucial for adaptation and evolution in prokaryotes and eukaryotes. It facilitates the spread of antibiotic resistance in bacteria, a significant concern in medicine. Bacteria can acquire resistance genes through HGT via plasmids, transposons and bacteriophages (viruses that infect bacteria), enabling them to survive antibiotic exposure. This transfer can occur between different bacterial species, leading to rapid dissemination of resistance. HGT allows organisms to evolve and adapt to changing environments, with mobile genetic elements accelerating the evolutionary pace.
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horizontal gene transfer, the transmission of DNA (deoxyribonucleic acid) between different genomes. Horizontal gene transfer is known to occur between different species, such as between prokaryotes (organisms whose cells lack a defined nucleus) and eukaryotes (organisms whose cells contain a defined nucleus), and between the three DNA-containing organelles of eukaryotesâthe nucleus, the mitochondrion, and the chloroplast. Acquisition of DNA through horizontal gene transfer is distinguished from the transmission of genetic material from parents to offspring during reproduction, which is known as vertical gene transfer.
Horizontal gene transfer is made possible in large part by the existence of mobile genetic elements, such as plasmids (extrachromosomal genetic material), transposons (âjumping genesâ), and bacteria-infecting viruses (bacteriophages). These elements are transferred between organisms through different mechanisms, which in prokaryotes include transformation, conjugation, and transduction. In transformation, prokaryotes take up free fragments of DNA, often in the form of plasmids, found in their environment. In conjugation, genetic material is exchanged during a temporary union between two cells, which may entail the transfer of a plasmid or transposon. In transduction, DNA is transmitted from one cell to another via a bacteriophage.
In horizontal gene transfer, newly acquired DNA is incorporated into the genome of the recipient through either recombination or insertion. Recombination essentially is the regrouping of genes, such that native and foreign (new) DNA segments that are homologous are edited and combined. Insertion occurs when the foreign DNA introduced into a cell shares no homology with existing DNA. In this case, the new genetic material is embedded between existing genes in the recipientâs genome.
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Compared with prokaryotes, the process of horizontal gene transfer in eukaryotes is much more complex, mainly because acquired DNA must pass through both the outer cell membrane and the nuclear membrane to reach the eukaryoteâs genome. Subcellular sorting and signaling pathways play a central role in the transport of DNA to the genome.
Prokaryotes can exchange DNA with eukaryotes, although the mechanisms behind this process are not well understood. Suspected mechanisms include conjugation and endocytosis, such as when a eukaryotic cell engulfs a prokaryotic cell and gathers it into a special membrane-bound vesicle for degradation. It is thought that in rare instances in endocytosis, genes escape from prokaryotes during degradation and are subsequently incorporated into the eukaryoteâs genome.
Horizontal gene transfer plays an important role in adaptation and evolution in both prokaryotes and eukaryotes. For example, the transfer of a gene encoding a unique metabolic enzyme from a species of Pasteurella bacteria to the protozoan parasite Trichomonas vaginalis is suspected to have facilitated the latter organismâs adaptation to its animal hosts. Likewise, the exchange of a gene from a human cell to the bacterium Neisseria gonorrhoeaeâa transfer that appears to have occurred relatively recently in the bacteriumâs evolutionâmay have enabled the organism to adapt and survive in humans. Scientists have proposed too that the recent evolution of the methylaspartate pathway of metabolism in the halophilic (salt-loving) archaean Haloarcula marismortui originated with the organismâs acquisition of a specialized set of genes via horizontal transfer.