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What is Horizontal Gene Transfer?
Virtually all organisms can disseminate genetic material via vertical gene transfer in which genetic information is transmitted from parents to offspring. In contrast, the process of horizontal gene transfer — or lateral gene transfer — is not common to all species. In this type of gene transfer, genetic material is transmitted between organisms that are not parent and offspring. Instead, the two organisms are usually unrelated, and are often of different species.
Most eukaryotic organisms acquire genetic material mainly via vertical gene transfer, during which DNA recombination occurs. In contrast, it is thought that horizontal gene transfer is the most common way in which single-celled organisms, bacteria in particular, acquire new genetic material. This is important because bacteria reproduce without sexual recombination; therefore horizontal transfer allows bacterial species to maintain diversity.
Horizontal gene transfer in bacteria is a common phenomenon. There are three ways in which bacteria can exchange genetic material horizontally. All three of these occur naturally and can also be carried out in the laboratory to genetically engineer bacteria with new properties, such as the ability to synthesize non-native proteins.
Transformation is a process in which bacteria ingest naked DNA or RNA molecules and express them within the cell. In transduction, genetic material is transferred by bacteriophages, which are viruses that infect bacteria. Finally there is bacterial conjugation, in which genetic material, often plasmids, is transferred via intercellular contact. Conjugation is mediated by transposons and plasmids, two types of genetic material which are distinct from and independent of the bacterial genome.
There is some evidence that viruses can also transmit genetic information via horizontal gene transfer. One of the strongest indicators involves viruses called Mimivirus, Mamavirus, and Sputnik. Both Mimivirus and Mamavirus are known hosts of Sputnik, and a small number of genes are common to all three species. It is thought that Sputnik transferred genes between its two host viruses at some point during the evolutionary history of these three organisms.
Certain eukaryotes, including species of fungi, insects, and plants, also engage in horizontal gene transfer. One of the most well-known examples is of horizontal genetic transfer between bacteria and Saccharomyces cerevisiae, a species of yeast. Another example of genetic transfer between eukaryotes involves the azuki bean beetle and a bacteria called Wolbachia. In the plant world, parasites of a plant family called Rafflesiaceae have transferred genetic information to their hosts, and a species of algae has transferred genetic material to a species of sea slug that preys on the algae.
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Discussion Comments
@jcraig - If it is remotely possible, I'm sure people are working on it. From the way the article describes it, I'm sure it would be hard for a bacteria and human cells to interact on their own, but with a little human intervention it might be possible.
I know scientists are able to grow human skin in labs now, so I guess anything is possible. It would be really neat if researchers could find a way to use bacteria to grow cells that we could put back into our bodies.
Along the same lines, something I'm thinking about now is horizontal gene transfer and antibiotic resistance. I guess this could work both ways where we may be more or less susceptible to different infections depending on what was put into our bodies.
I know in a lot of tree species, especially hickories, there is a lot of crossbreeding between different species. It seems to be much more common in plants than animals.
I was curious how horizontal gene transfer could be incorporated into humans. Maybe this has already been done, but I have not heard about it. Could you take cells with human genes and match them with a bacteria or eukaryote and create something that we could put back into our bodies?
I don't know if this is even possible, but it seems like someway it might be usable in fixing various genetic defects or diseases.
@cardsfan27 - I was curious about the same thing when I was reading this article, but I was thinking about a liger. If I remember correctly, they are both in the same genus, but are different species.
Clearly, lions and tigers don't reproduce naturally in the wild, but I'm pretty sure when ligers are bred, there is not genetic manipulation that goes on, they just artificially inseminate one species with the other and let normal growth occur. I guess the same reasoning would be true for mules, too, which are crosses between horses and donkeys.
Does horizontal gene transfer have to refer to a natural process, or does it also include genetic engineering of different species by humans? Specifically, I am thinking about genetically engineered corn and soybean plants that are resistant to the herbicide Roundup. In this case, scientists have physically put a Roundup resistant gene into the plants and reproduced them.
I'm not sure if the original gene came from the plants themselves, but I am wanting to say the gene was discovered in one plant and transferred to other more commercial plants.
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