Horizontal gene transfer

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Horizontal gene transfer (HGL), also called Lateral gene transfer (LGT), is the process of transferring genetic material between different species, or across broad taxonomic categories.

Main mechanisms of gene transfer in prokaryotes

HGT between distant microbial phyla is mediated by bacteriophages, plasmids, transposons, and specialized DNA uptake mechanisms. These mechanisms usually categorized with the following:

  • Bacterial transformation , the genetic alteration of a cell resulting from the introduction, uptake and expression of foreign genetic material, generally DNA (see this animation with audio explanation). This process is relatively common in certain naturally transformable bacteria, such as the soil bacterium Bacillus subtilis. Transformation is often used as a biotechnology to insert novel genes into bacteria for scientific research experiments, or for industrial or medical applications.
  • Transduction, the process in which bacterial DNA is moved from one bacterium to another by a bacterial virus (a bacteriophage, commonly called a phage).
  • Bacterial conjugation ( or mating), a process in which a living bacterial cell transfers genetic material through direct cell-to-cell contact (see the animation conjugation in Escherichia coli).

Main mechanisms of gene transfer in eukaryotes

Documented examples of HGT in eukaryotes

Protein Case Reference
Glucose phosphate isomerase gpi from E. coil was inherited from a relative of the

dicot Clarkia ungulata

Fe superoxide dismutase The Fe SOD from the protist Entamoeba histolytica

has prokaryotic origins

Aldolase Class 11 Aldolase from yeast shows affinity to that

from E. coil

Cytochrome c The protein from Arabidopsis thaliana is of fungal


Xylanase Rumoncoccus-like gene is found in a rumen fungus [5]
Thioredoxin Thioredoxin-m in plants has a bacterial origin [6]


gapdhA from E. coli and Anabaena have an affinity

with eukaryotic gapC

Elongation Factor Tu rufA in Arabidopsis is from its endosymbiont [9]
Ribosomal proteins L21

and L22

L2l and L22 in some plants is from its endosymbiont [10]

The risks of horizontal gene transfer

  1. Antibiotic resistance genes spreading to pathogenic bacteria.
  2. Disease-associated genes spreading and recombining to create new viruses and bacteria that cause diseases.
  3. Transgenic DNA inserting into human cells, triggering cancer.


  1. Smith MW, Feng DF, Doolittle RF. 1992. Evolution by acquisition: the case for horizontal gene transfers. Trends Biochem. Sci. 17:489—93
  2. Smith MW, Feng DF, Doolittle RF. 1992. Evolution by acquisition: the case for horizontal gene transfers. Trends Biochem. Sci. 17:489—93
  3. Smith MW, Feng DF, Doolittle RF. 1992. Evolution by acquisition: the case for horizontal gene transfers. Trends Biochem. Sci. 17:489—93
  4. Kemmerer EC, Lei M, Wu R. 1991. Structure and molecular evolutionary analysis of a plant cytochrome c gene: surprising implications for Arabidopsis thaliana. J. Mol. Evol. 32:227—37
  5. Gilbert HJ, Hazlewood GP, Laurie JI, 0rpin CG. Xue GP. 1992. Homologous catalytic domains in a rumen fungal xylanase: evidence for gene duplication and prokaryotic origin. Mol. Microbiol. 6:2065—72
  6. Hartman H, Syvanen M, Buchanan BB. 1990. Contrasting evolutionary histories of chloroplast thioredoxins f and m. Mol. Biol. Evol. 7:247—54
  7. Doolittle RF, Feng DF, Anderson KL, Alberro MR. 1990. A naturally occur ring horizontal gene transfer from a eukaryote to a prokaryote. J. Mol. Evol. 31:383—88
  8. Martin W, Brinkmann H, Savonna C, Cerff R. 1993. Evidence for a chimeric nature of nuclear genomes: eubacterial origin of eukaryotic glyceraldehyde-3- phosphate dehydrogenase genes. Proc. Natl. Acad Sci. USA 90:8692—6
  9. Baldauf SL, Manhart JR. Palmer JD. 1990. Evolutionary transfer of the chloroplast tufA gene to the nucleus. Nature 9. 344:262—65
  10. Gantt JS, Baldauf SL, Calie PJ, Weeden NF. Palmer JD. 1991. Transfer of rpl22 to the nucleus greatly preceded its loss from the chloroplast and involved the gain of an intron. EMBO J. 10:3073—78