Biological Sciences
Bacterial Transformation
Bacterial transformation is a process in which bacteria take up foreign genetic material, such as plasmid DNA, from their environment and incorporate it into their own genome. This technique is widely used in genetic engineering to introduce specific genes into bacteria for various purposes, such as producing proteins or studying gene function.
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9 Key excerpts on "Bacterial Transformation"
- Tina M. Henkin, Joseph E. Peters(Authors)
- 2020(Publication Date)
- ASM Press(Publisher)
chapter 3 . In this chapter, we concentrate on the mechanism of transformation in various bacteria and its relationship to other biological phenomena.Natural Transformation
Some types of bacteria are naturally transformable , which means that they can take up DNA from their environment without requiring special chemical or electrical treatments to make them more permeable. Even naturally transformable bacteria are not always capable of taking up DNA and in most cases do so only at certain stages in their life cycle or under certain growth conditions. Bacteria that can take up DNA are said to be competent , and bacteria that are naturally capable of reaching this state are said to be naturally competent .Naturally competent transformable bacteria were originally found in several genera, including members of the Firmicutes, such as Bacillus subtilis, a soil bacterium, and Streptococcus pneumoniae, which causes throat infections, and Proteobacteria, such as Haemophilus influenzae, a causative agent of pneumonia and spinal meningitis, and Neisseria gonorrhoeae, which causes gonorrhea. More recently, natural transformation has been uncovered not only in close relatives of the initial model systems, but also in Helicobacter pylori, a stomach pathogen; Acinetobacter baylyi, another soil bacterium; marine cyanobacteria including Synechococcus; Vibrio cholerae, which causes cholera; Thermus thermophilus, an extreme thermophile; and Deinococcus radiodurans, an organism resistant to high levels of radiation. Genome sequencing has revealed that many organisms that have not been demonstrated to be naturally transformable contain some of the genes known to be involved in competence in other species, suggesting that some of these organisms may be transformable under certain conditions or that they have lost this property; the number of transformable organisms is increasing rapidly as new approaches for inducing competence are uncovered (see Johnston et al
eBook - PDF- Papita H Gourkhede(Author)
- 2023(Publication Date)
- Arcler Press(Publisher)
Although bacteria can acquire additional genes through transformation and transduction, this is often a more infrequent transfer between bacterium of the same or closely linked species. 3.2. TRANSFORMATION Pieces of DNA produced by donor bacterium are picked up directly from the extracellular environment by receiver bacterium during transformation. Recombination happens between single molecules of transformed DNA and receiving bacterial chromosomes. DNA molecules must be at least 500 nucleotides long to be active in transformation, and transforming activity is swiftly eliminated by treating DNA with deoxyribonuclease. Transforming DNA molecules are very tiny pieces of the bacterial chromosome. Gene co-transformation is therefore improbable unless they are so closely related that they may be expressed on a single DNA fragment. Transformation was identified in Streptococcus pneumoniae and is also seen in Haemophilus, Neisseria, Bacillus, and Staphylococcus. The capacity of bacteria to take up extracellular DNA and get converted, known as competence, changes with the organism’s physiologic condition. Genetic Information Transfer 67 Many bacteria that are normally incapable of taking up DNA can be coaxed to do so using laboratory manipulations such as calcium shock or exposure to a high-voltage electrical pulse (electroporation). DNA absorption in some bacteria (including Haemophilus and Neisseria) is dependent on the presence of particular oligonucleotide sequences in the transforming DNA, but not in others (including Streptococcus pneumoniae). Competent bacteria can also accept intact bacteriophage DNA or plasmid DNA, which can then reproduce as extrachromosomal genetic components in the recipient bacterium. Unless it becomes part of a replicon by recombination, a portion of chromosomal DNA from a donor bacterium normally cannot reproduce in the receiving bacterium. Traditionally, the characterization of the “transforming principle” of S.
eBook - ePubAdvanced Molecular Biology
A Concise Reference
- Richard Twyman(Author)
- 2018(Publication Date)
- Garland Science(Publisher)
Chapter 10Gene Transfer in Bacteria
Fundamental concepts and definitions- Gene transfer describes the introduction of genetic information into a cell from an exogenous source (ultimately, another cell). This process occurs naturally in both bacteria and eukaryotes, and may be termed horizontal or lateral genetic transmission to distinguish it from the transmission of genetic information from parent to offspring, which is vertical genetic transmission.
- Intraspecific gene transfer facilitates genetic mixing in asexual species and thus mimics the effects of sexual reproduction. Such parasexual exchange mechanisms have been exploited to map prokaryote genomes analogously to meiotic mapping (q.v.) in eukaryotes. Interspecific gene transfer can also occur, and is a natural mechanism of transgenesis (q.v.). Interspecific gene transfer is an important evolutionary process and has been responsible for some of the most fundamental evolutionary events (e.g. the endosymbiont origin of eukaryotic organelles) as well as facilitating specific interactions between bacteria and eukaryotes (e.g. tumor-induction by Agrobacterium tumorfaciens; q.v. Ti plasmid).
- The source of the transferred information is the donor and the genetic information transferred is the exogenote (exogenous genome, usually only a fragment of the donor genome). The target of the gene transfer, the recipient, possesses the endogenote (endogenous genome). If the exogenote is homologous to part of the endogenote, gene transfer will make the recipient cell partially diploid (a merozygote), in which case recombination can occur, which may involve allele replacement (marker exchange).
- There are four major mechanisms of gene transfer in bacteria: cell fusion, conjugation, transformation and transduction (Table 10.1 ).
eBook - ePubMolecular Biology
Academic Cell Update Edition
- David P. Clark(Author)
- 2012(Publication Date)
- Academic Cell(Publisher)
There are three different mechanisms for new genes to be added to bacteria: conjugation, transduction, and transformation. Transformation is the transfer of naked DNA from the environment into the bacterial cell. Transformation only occurs in competent bacteria, so this technique occurs only under certain circumstances in the environment, and it is mainly exploited by researchers in the laboratory. In the environment, transformation happens when bacteria of the same kind reach a certain density and release pheromones that induce expression of DNA uptake proteins. In the lab, transformation occurs because the cell wall and membrane are damaged, and DNA is able to get into the cytoplasm. Basically, bacteria are made competent by chilling them in the presence of calcium ions which loosens the structures of their cell wall and membrane. Heat shock then disrupts the wall and membrane and allows the DNA into the cytoplasm. Alternatively, bacteria are made competent by electroporation, where a high voltage shock induces the bacteria to take up naked DNA. The DNA taken up by competent bacteria must have an origin of replication for it to survive as the bacteria grow, so usually plasmids are used in transformation. If linear pieces of DNA are transformed into bacteria, these can only survive cell division if they have regions that are homologous to the bacterial chromosome. On rare occasions, the homologous regions will line up, and recombination will replace the bacterial chromosome region with the linear transformed DNA. Recombinants will then have the transformed linear DNA. When naked viral DNA is used in transformation, bacterial scientists call this transfection. (Note: The term, transformation, can also mean changing normal cells into cancer cells, and the term, transfection, can also mean the artificial introduction of foreign DNA into cultured animal cells.)Transformation was used to confirm that DNA was the genetic material by Oswald Avery in 1944. He used the naked DNA from two different Streptococcus pneumonia strains, one formed a smooth colony and the other formed a rough looking colony on agar plates. The smooth colony variant was more virulent, and would cause mice to die of pneumonia. Avery isolated the DNA from the smooth variant, and transformed it into a rough variant of S. pneumonia. The transformant had a smooth coat, and caused mice to die of pneumonia, suggesting that the DNA alone was the agent to change the bacteria from rough and avirulent to smooth and virulent.In the second type of genetic exchange, bacteria can get new genes from viruses in a process called transduction. Here a virus infects one bacterium, and when it packages all its progeny, occasionally, a piece of bacterial chromosome is packaged in the phage head rather than the viral genome. This phage can infect another host cell where it will inject its piece of chromosomal DNA rather than the viral genome. Although the chromosomal DNA is linear, if it has any homology with the new host chromosome, recombination can integrate the new DNA into the recipient cell, changing the genome permanently. In the laboratory, any bacteria that gets phage genome is killed by lysis, and all those cells that get the defective phage will survive and divide as usual.
eBook - ePubGenetic Engineering
Volume 1: Principles Mechanism, and Expression
- Tariq Ahmad Bhat, Jameel M. Al-Khayri, Tariq Ahmad Bhat, Jameel M. Al-Khayri(Authors)
- 2023(Publication Date)
- Apple Academic Press(Publisher)
Processes of introducing and incorporating exogenous DNA into host cells with a stable genetic transformation have a lot of significance in cellular and molecular biology. These goals of introducing foreign DNA into the host cells can be achieved by using several methods such as transformation, transduction, and transfection, which utilizes the incorporation of DNA into the host cell by a host-specific vector or through vector-free transformation, which primarily depends on the mechanism used for the experiment and objectives of the study. Several chemical, biological, and physical methodologies can be used depending upon the experimental needs and host cell nature. An ideal approach is to choose a method that have high transformation efficiency, low host cell toxicity, and minimum effect on the normal physiology of the transformed cells._____________________ Genetic Engineering, Volume 1: Principles, Mechanism, and Expression. Tariq Ahmad Bhat & Jameel M. Al-Khayri (Eds.) © 2023 Apple Academic Press, Inc. Co-published with CRC Press (Taylor & Francis)4.2 Difference Between Transformation, Transfection, and Transduction
Transformation, transduction, and transfection are some commonly used terminologies that are opted when manipulated DNA is introduced into host cells. The main differences between these terminologies are given below to evade misperception about them.When recombinant DNA (rDNA) is introduced into prokaryotic competent cells by using non-viral gene transfer methods, it is usually termed as transformation. This process is not likely to happen naturally in an environment, but scientists have been harnessing the method in laboratories for so long to get eugenic aims. In this method, cells are made competent to intake foreign DNA by using several chemicals and physical means. Later on, transformed cells can be distinguished from non-transformed ones by any selectable marker gene, e.g., antibiotic-resistant genes, available in the vector.Transfection, on the other hand, is a term applied when transferring a foreign DNA molecule into eukaryotic cells, by using non-viral means. Unlike transformation where the host cell is of prokaryotic origin, transfection deals with the uptake of manipulated DNA into eukaryotic cells. Here, eukaryotic cell membrane is made permeable by using chemical and physical methods for foreign DNA incorporation. However, methodologies used in this case are different from those of transformation. Cationic lipids, micelles, lasers, or even particle guns are some common methods used for lab-cultured eukaryotic cell transformation.
- J. A. V. Butler(Author)
- 2016(Publication Date)
- Pergamon(Publisher)
In summary, then, the susceptibility to transformation appears to require a special, otherwise unknown, physiological state of the receptor cell. This susceptibihty may mean not only the admission of transforming principle into the cell, but its further acceptability inside the cell. It is logical to assume that the transforming principle (DNA) upon admission does not remain loose (in solution). If analogy can be drawn to higher organisms, bacteria may also possess chromosomes 93 BIOPHYSICAL PROPERTIES OF TRANSFORMING PRINCIPLES (DE LAMATER (54) ) which contain all* the DNA of the cell, in the form of nucleoproteins, in the structures corresponding to genetical loci: only chromosomal DNA may enjoy the benefit of orderly reproduction through chromosomal apparatus. Thus upon entering the susceptible cell, the DNA may become fixed to the locus, probably by precipi-tating as nucleoprotein. That some sort of fixation or precipitation seems necessary has been postulated recently by demonstration that the molecule of DNA of E. coli is in solution actually longer than the cell of E. coltf. (ROWEN and NORMAN ( 5 5 ) ). Another phenomenon, which may involve both admission to the cell and the acceptability inside the cell, is the phenomenon of competition. ALEXANDER, LEIDY and HAHN ( 5 2 ) have demonstrated that when the transforming principle from H. influenzae cells type a was mixed, in a certain proportion, with one from type b, and the mixture used to transform R cells, the transformed cells represented a mixture of cells of type a and 6, in a proportion similar to that used for preparation of the mixture of transforming principles a and b. Similar results were obtained when mixing the transforming principles b and c. Under appropriate experimental conditions, prior exposure to high concentra-tion of transforming principle of one type can completely exclude subsequent transforming principle from effecting transformation.
eBook - ePub- David P. Clark(Author)
- 2009(Publication Date)
- Academic Cell(Publisher)
recipient cell that receives the DNA.The transfer of genes between bacteria fulfils a similar evolutionary purpose to the mingling of genes during sexual reproduction in higher organisms. However, mechanistically it is very different. Consequently, some scientists regard bacterial gene transfer as a primitive or aberrant form of sex, whereas others believe that it is quite distinct and that use of the same terminology is misleading.Molecular biologists use bacteria together with their plasmids and viruses to carry most cloned genes, whether they are originally from cabbages or cockroaches. Consequently, an understanding of bacterial gene transfer is needed to understand the genetic engineering of plants and animals. Gene transfer in bacteria occurs by three basic mechanisms. Only in conjugation are genes transferred by cell-to-cell contact. In transduction , genes are transferred inside virus particles, and in transformation , free molecules of DNA are taken up by a bacterial cell. Before considering these three mechanisms in detail, we will discuss what happens to the DNA after uptake, as similar considerations apply in all three cases.Gene transfer between bacteria may involve uptake of naked DNA, transport of DNA inside virus particles or transfer of DNA from cell to cell.Fate of the Incoming DNA after Uptake
Irrespective of its mode of entry, DNA that enters a bacterial cell has one of three possible fates. It may survive as an independent DNA molecule, it may be completely degraded, or part may survive by integration or recombination with the host chromosome before the rest is degraded.For incoming DNA to survive inside a bacterial cell as a self-replicating DNA molecule, it must be a replicon. In other words it must have its own origin of replication and lack exposed ends. For survival in the vast majority of bacteria, this means that it must be circular. In those few bacteria, such as Borrelia and Streptomyces (see Ch. 5 ) with linear replicons, the ends must be properly protected. In eukaryotes, long-term survival of a linear DNA molecule requires a replication origin, a centromere sequence, and telomeres to protect the ends (see Ch. 5
eBook - PDF- H W Doelle(Author)
- 1994(Publication Date)
- WSPC(Publisher)
In natural transformation, the DNA comes from a donor bacterium. This process is random, and any portion of the genome may be transferred. Cells that are in a state in which they can be trans-formed by DNA in their environment are referred to as compe-tent cells. If the entry into the competent state is encoded by chromosomal genes and signalled by certain environmental conditions, these bacteria are undergoing a natural transformation. If the cells have to be exposed to a variety of highly a r t i f i c i a l treatment, e.g. high concentrations of divalent cations, to be made competent, the system of transformation is referred to as a r t i f i c i a l transformation. Bacterial Genetics 4.1.1. Natural transformation in gram-positive cells 81 Gram-positive bacteria (e.g. Streptococcus) in culture become competent rapidly during the log phase of growth. The conversion of noncompetent into competent cells is mediated by a small protein, referred to as the competence factor. Competence develops as soon as the population density and hence the concentration of competence factor reach a certain critical value. With the help of the competence factor, which consists normally of a set of 12 proteins, competent cells can absorb double-stranded DNA to their outer surface and cleave i t through the action of surface-bound enzymes into smaller fragments. One strand of the fragment is diges-ted by a nuclease whereas the other enters the cell with the help of a competence specific DNA binding protein. 4.1.2 Natural transformation in gram-negative cells The transformation in Haemophilus influenzae, a gram-negative bacterium, differs from that of Streptococcus in several respects. No competence factor is produced that triggers the development of the competent state. Cells become competent as a consequence of growth in rich media. Furthermore, there are two additional ways in which both systems differ from each other.
- Kumar, Har Darshan(Authors)
- 2021(Publication Date)
- Daya Publishing House(Publisher)
The following overall conclusions and implications may be made about the three major mechanisms of gene transfer ( i.e. , transformation, conjugation, and transduction) in natural environments. 1.Gene transfer in two directions has been shown by: (1) cell–to–cell contact transformation; (2) retrotransfer in conjugation; and (3) reciprocal chromosomal transduction. This means that gene transfer by all these mechanisms could occur bidirectionally in the environment. 2.In some bacteria, there are additional mechanisms for gene transfer in nature. For example, streptomycetes can fuse their hyphae (anastomosis), resulting in gene exchange. Transposition, in which specific mobile molecules of DNA change position within or among This ebook is exclusively for this university only. Cannot be resold/distributed. a bacterial genome and plasmids, may also be important in gene transfer in the environment, as indicated by reports of transposon– mediated conjugation. Lightning in natural environments may possibly electroporate indigenous cells in nature. 3.The traditional definitions of the three major mechanisms are gradually becoming more and more ambiguous as the result of such discoveries as cell-to-cell transformation, capsduction, transposon– mediated conjugation, and retrotransfer. 4.Interactions and synergy among and between the mechanisms of gene transfer are possible in the environment. Each mechanism is not entirely independent but may interact with others and may be used alternatively by the same bacteria or phages, depending on the environmental conditions. Bacteria in the environment live as mixtures and in a community rather than as single species or strains, as on an agar plate in the laboratory. Therefore, several mechanisms of gene transfer may be acting simultaneously in a mixed bacterial community, and ambient environmental conditions may favor one or another mechanism.
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