horizontal gene transfer

Examples of horizontal gene transfer in the following topics:

• Pathogenicity Islands and Virulence Factors

  • Pathogenicity islands (PAIs) are a distinct class of genomic islands acquired by microorganisms through horizontal gene transfer.
  • Pathogenicity islands (PAIs) are a distinct class of genomic islands acquired by microorganisms through horizontal gene transfer.
  • Cryptic mobility genes may also be present, indicating the provenance as transduction.
  • PAIs are transferred through horizontal gene transfer events such as transfer by a plasmid, phage, or conjugative transposon.
  • They may be located on a bacterial chromosome or may be transferred within a plasmid.

• Pathogenicity Islands

  • Pathogenicity islands (PAIs) are a distinct class of genomic islands acquired by microorganisms through horizontal gene transfer.
  • Cryptic mobility genes may also be present, indicating the provenance as transduction.
  • They are transferred through horizontal gene transfer events such as transfer by a plasmid, phage, or conjugative transposon .
  • They may be located on a bacterial chromosome or may be transferred within a plasmid.
  • Pathogenicity islands are transferred horizontally, this details some of the ways that occurs.

• Plasmids and Lysogeny

  • In addition, plasmid DNA provides a mechanism by which horizontal gene transfer can occur, contributing to antibiotic resistance.
  • Horizontal gene transfer is a major mechanism promoting bacterial antibiotic resistance, as the plasmid DNA can transfer genes from one species of bacteria to another.
  • The plasmid DNA which is transferred often has developed genes that encode for resistance against antibiotics.
  • The process of horizontal gene transfer can occur via three mechanisms: transformation, transduction and conjugation.
  • There are three mechanisms by which horizontal gene transfer can occur.

• Gene Transfer in Archaea

  • This phenomenon is described as horizontal gene transfer.
  • Horizontal gene transfer (HGT) refers to the transfer of genes between organisms in a manner other than traditional reproduction.
  • Also termed lateral gene transfer, it contrasts with vertical transfer, the transmission of genes from the parental generation to offspring via sexual or asexual reproduction.
  • Archaea show high levels of horizontal gene transfer between lineages.
  • Taken together it is clear that gene transfer happens in Archaea, and probably is similar to horizontal gene transfer seen in the other domains of life.

• Introduction to Plasmids

  • Plasmids can be considered part of the mobilome because they are often associated with conjugation, a mechanism of horizontal gene transfer.
  • Unlike viruses, they are naked DNA and do not encode genes necessary to encase the genetic material for transfer to a new host, though some classes of plasmids encode the sex pilus necessary for their own transfer.
  • Plasmid host-to-host transfer requires direct mechanical transfer by conjugation, or changes in incipient host gene expression allowing the intentional uptake of the genetic element by transformation.
  • Rather, plasmids provide a mechanism for horizontal gene transfer within a population of microbes and typically provide a selective advantage under a given environmental state.
  • Plasmids may carry genes that provide resistance to naturally occurring antibiotics in a competitive environmental niche, or the proteins produced may act as toxins under similar circumstances.

• Agrobacterium and Crown Gall Disease

  • Argobacterium causes Crown Gall Disease by transferring a DNA plasmid to the host plant, causing the host to make nutrients for it.
  • A. tumefaciens can transfer part of its DNA to the host plant, through a plasmid - a bacterial DNA molecule that is independent of a chromosome.
  • Bacteria normally use plasmids for horizontal gene transfer, so they can share genes with related bacteria to help them cope with stressful environments.
  • The new plasmid genes are expressed by the plant cells, and cause them to secrete enzymes that produce the amino acids octopine or nopaline.
  • It also carries genes for the biosynthesis of the plant hormones, auxin and cytokinins, and for the biosynthesis of opines, providing a carbon and nitrogen source for the bacteria.

• Shared Features of Archaea and Eukaryotes

  • Archaea possess genes and several metabolic pathways that are more closely related to those of eukaryotes than prokaryotes.
  • Complicating factors include claims that the relationship between eukaryotes and the archaeal phylum Crenarchaeota is closer than the relationship between the Euryarchaeota and the phylum Crenarchaeota, and the presence of archaean-like genes in certain bacteria, such as Thermotoga maritima, from horizontal gene transfer.
  • Despite this visual similarity to bacteria, archaea possess genes and several metabolic pathways that are more closely-related to those of eukaryotes, notably the enzymes involved in transcription and translation.

• Aquifex, Thermocrinis, and Related Bacteria

  • The presence of the insertion in the Thermotogae species may be due to a horizontal gene transfer.
  • In the 16S rRNA gene trees, the Aquificae species branch in the proximity of the phylum Thermotogae (another phylum comprising hyperthermophilic organisms) close to the archaeal-bacterial branch point.
  • However, a close relationship of the Aquificae to Thermotogae, and the deep branching of Aquificae, is not supported by phylogenetic studies based upon other gene/protein sequences and also by conserved signature indels in several highly-conserved universal proteins.
  • Comparison of the A. aeolicus genome to other organisms showed that around 16% of its genes originated from the Archaea domain.
  • A. aeolicus is also known as one of the few bacterial species capable of doing gene silencing.

• Phenotypic Analysis

  • This horizontal gene transfer, coupled with a high mutation rate and many other means of genetic variation, allows microorganisms to swiftly evolve (via natural selection) to survive in new environments and respond to environmental stresses.
  • These plasmids can be transferred between cells through bacterial conjugation.
  • This uncertainty was due to the lack of distinct structures in most bacteria, as well as lateral gene transfer between unrelated species.
  • Due to lateral gene transfer, some closely related bacteria can have very different morphologies and metabolisms.
  • To overcome this uncertainty, modern bacterial classification emphasizes molecular systematics, using genetic techniques such as guanine cytosine ratio determination, genome-genome hybridization, as well as sequencing genes that have not undergone extensive lateral gene transfer, such as the rRNA gene.

• Phylogenetic Analysis

  • This uncertainty was due to the lack of distinctive structures in most bacteria, as well as lateral gene transfer between unrelated species.
  • As more genome sequences become available, scientists have found that determining these relationships is complicated by the prevalence of lateral gene transfer (LGT) among archaea and bacteria.
  • Due to lateral gene transfer, some closely related bacteria can have very different morphologies and metabolisms.
  • To overcome this uncertainty, modern bacterial classification emphasizes molecular systematics, using genetic techniques such as guanine cytosine ratio determination, genome-genome hybridization, as well as sequencing genes that have not undergone extensive lateral gene transfer, such as the rRNA gene.
  • This approach is expected to have an increased resolving power due to the large number of characters analyzed and a lower sensitivity to the impact of conflicting signals (i.e. phylogenetic incongruence) that result from eventual horizontal gene transfer events.