Horizontal gene transfer

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Exchange of the F plasmid by conjugation
Modern family tree of life. It is divided into three domains, according to the results of Carl Woese and others. The horizontal gene transfer by chloroplasts and mitochondria can be found in the lower center of the figure. According to Woese, horizontal gene transfer played the decisive role in the development of the three domains from a consortium of primordial cells with a very small genome (Fig. Below).

Horizontal gene transfer ( HGT ) or lateral gene transfer ( LGT ) denotes a transfer of genetic material not along the line of descent, i.e. not from one generation to the next, but “horizontally” from one organism to another that already exists. In contrast, the vertical gene transfer takes place from ancestors to descendants , the gene transfer from gene residues that has already been detected over time is called anachronistic evolution . Natural lateral gene transfer is mainly observed in prokaryotes, especially in bacteria that pass on part of their genetic material to another individual by conjugation. In contrast to vertical transmission , in which the genetic material of a pathogen is transferred from one infected generation to the next (e.g. in Wolbachia pipientis ), horizontal gene transfer is not linked to a reproductive process. The genes are often in a mobile form (a vector such as bacteriophages or plasmids ). For example, when bacteria are conjugated, genetic material is transferred between individuals of the same species or between individuals of different species, regardless of reproduction processes. A previously replicated plasmid is transferred to a recipient cell. This results in an enrichment of the recipient organism with genetic information.


In the theory of evolution, horizontal gene transfer is therefore a way of explaining leaps in development, especially in microorganisms . Horizontal gene transfer enables accelerated adaptation to changing environmental conditions, e.g. B. by passing on antibiotic resistance or a virulence factor , sometimes also grouped in so-called. Pathogenicity islands .

Horizontal gene transfer complicates the determination of family trees by molecular clocks . On the other hand, it is postulated that horizontal gene transfer promotes the maintenance of a universal biochemistry of life and consequently the universality of the genetic code. In other words: the horizontal gene transfer monitors the universality of the genetic code and forces it into a lingua franca of life on earth. In this way genetic exchange or the diffusion of biological novelty through the biosphere can take place.

Since the complete genome of a wide variety of bacteria and archaeates has been sequenced , gene transfer between distantly related organisms has also been shown to play a major role, especially when they inhabit overlapping ecological niches . In mesophilic bacteria, which thrive best at temperatures between around 20 and 45 ° C and live anaerobically , it was found that 16% of the genome comes from horizontal gene transfer. One third of the genes of enzymes of the chemotrophic metabolism derived from a gene transfer, while ribosomal proteins by a factor of 150 horizontal rare were exchanged. The proportion of genes transferred by gene exchange is lower by a factor of about 2 in aerobic microorganisms. With them, too, the HGT has made a significant contribution to their adaptability and the variety of substrates used by microorganisms .

Gene transfer from bacteria to the archaea also played an important role . About 5% of the genome of the methanogenic organism Methanosarcina is of bacterial origin. Through the transferred genes, these organisms have acquired the ability to use acetate and convert it into methane . It is possible that this ability of the methanogenic archaeates acquired through HGT contributed to the climatic catastrophe around 252 million years ago ( Permian-Triassic boundary ), which at that time led to the largest known mass extinction in Earth's history.

The two photosystems of oxygenic photosynthesis come from different organisms

Even more decisive in the history of the earth was the formation of molecular oxygen and its accumulation in the earth's atmosphere. Cyanobacteria were responsible for this oxygenic photosynthesis , releasing O 2 from water using light energy . To do this, they use a chemiosmotically coupled electron transport chain in their membranes . It consists of two systems that were developed separately from unrelated bacteria and then came to an ancestor of the cyanobacteria via HGT.

Genetic engineering

Horizontal gene transfer is an important method in genetic engineering to generate transgenic organisms. Different methods have been used successfully for prokaryotes and eukaryotes , respectively. In prokaryotes, conjugation , transduction and transformation are used. In eukaryotes, a transfection can be carried out as an equivalent to transformation in prokaryotes .

Gene therapy

The introduction of genetic material into human germ cells, the so-called " germ line therapy ", for example to correct a genetic defect, is prohibited in Germany due to the high risks stemming from the Embryo Protection Act of 1991. The smuggling of therapeutically effective genetic material into the body cells of an already existing recipient organism (horizontal gene transfer) is permitted, is already being used successfully in individual areas and is referred to as somatic gene therapy .

Evidence and examples

The transfer of prokaryotic DNA to eukaryotes has so far been directly demonstrated in Agrobacterium tumefaciens (plant cells) and Bartonella henselae (human cells).

An example of a horizontal gene transfer at higher organisms is the transfer of genes for carotenoid - synthesis of a mushroom on the Acyrthosiphon pisum ( Acyrthosiphon pisum ).

Another example is the takeover of a cellulase gene by a branch of the Nematoda from their endosymbionts .

In 2012, Ricardo Acuña and colleagues found evidence that the coffee cherry beetle ( Hypothenemus hampei ) had acquired the HhMAN1 gene for the digestive enzyme mannanase by horizontal gene transfer from an as yet unidentified bacterium . The enzyme enables the beetle to break down and digest galactomannans , the most important storage carbohydrates in the coffee bean.

During a comprehensive search for bacterial genes in the now numerous openly accessible sequences of human genomes, bacterial genes that had been introduced into certain cancer cells were found, but in a few cases also in healthy cells.

See also

Individual evidence

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  19. Werner E. Mayer et al .: Horizontal gene transfer of microbial cellulases into nematode genomes is associated with functional assimilation and gene turnover. In: BMC Evolutionary Biology. Volume 11, No. 1, 2011, p. 13.
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