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''Agrobacterium'' is a
genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
of
Gram-negative Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wall ...
bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...
established by H. J. Conn that uses
horizontal gene transfer Horizontal gene transfer (HGT) or lateral gene transfer (LGT) is the movement of genetic material between Unicellular organism, unicellular and/or multicellular organisms other than by the ("vertical") transmission of DNA from parent to offsprin ...
to cause
tumors A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...
in plants. ''
Agrobacterium tumefaciens ''Agrobacterium radiobacter'' (more commonly known as ''Agrobacterium tumefaciens'') is the causal agent of crown gall disease (the formation of tumours) in over 140 species of eudicots. It is a rod-shaped, Gram-negative soil bacterium. Sympto ...
'' is the most commonly studied
species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
in this genus. ''Agrobacterium'' is well known for its ability to transfer DNA between itself and plants, and for this reason it has become an important tool for
genetic engineering Genetic engineering, also called genetic modification or genetic manipulation, is the modification and manipulation of an organism's genes using technology. It is a set of technologies used to change the genetic makeup of cells, including t ...
.


Nomenclatural History

Leading up to the 1990s, the genus ''Agrobacterium'' was used as a
wastebasket taxon Wastebasket taxon (also called a wastebin taxon, dustbin taxon or catch-all taxon) is a term used by some taxonomists to refer to a taxon that has the sole purpose of classifying organisms that do not fit anywhere else. They are typically defined ...
. With the advent of 16S sequencing, many ''Agrobacterium'' species (especially the marine species) were reassigned to genera such as ''
Ahrensia In taxonomy, ''Ahrensia'' is a genus of the Hyphomicrobiales.See the NCBIbr>webpage on Ahrensia Data extracted from the ''Ahrensia'' is named after the German microbiologist R. Ahrens. The cells are rod-shaped and motile. They are strictly ae ...
'', ''
Pseudorhodobacter In taxonomy, ''Pseudorhodobacter'' is a genus of the Rhodobacteraceae.See the NCBI The National Center for Biotechnology Information (NCBI) is part of the United States National Library of Medicine (NLM), a branch of the National Institutes ...
'', ''
Ruegeria In taxonomy, ''Ruegeria'' is a genus of the Rhodobacteraceae. This genus was formerly known as the marine '' Agrobacterium'' before they were reclassified in 1998. It bears in fact the name of Hans-Jürgen Rüger, a German microbiologist, for h ...
'', and ''
Stappia In taxonomy, ''Stappia'' is a genus of the Hyphomicrobiales The ''Hyphomicrobiales'' are an order of Gram-negative Alphaproteobacteria. The rhizobia, which fix nitrogen and are symbiotic with plant roots, appear in several different famili ...
''. The remaining ''Agrobacterium'' species were assigned to three biovars: biovar 1 (''
Agrobacterium tumefaciens ''Agrobacterium radiobacter'' (more commonly known as ''Agrobacterium tumefaciens'') is the causal agent of crown gall disease (the formation of tumours) in over 140 species of eudicots. It is a rod-shaped, Gram-negative soil bacterium. Sympto ...
''), biovar 2 (''Agrobacterium rhizogenes''), and biovar 3 (''Agrobacterium vitis''). In the early 2000s, ''Agrobacterium'' was synonymized with the genus ''
Rhizobium ''Rhizobium'' is a genus of Gram-negative soil bacteria that fix nitrogen. ''Rhizobium'' species form an endosymbiotic nitrogen-fixing association with roots of (primarily) legumes and other flowering plants. The bacteria colonize plant cells ...
''. This move proved to be controversial. The debate was finally resolved when the genus ''Agrobacterium'' was reinstated after it was demonstrated that it was phylogenetically distinct from ''Rhizobium'' and that ''Agrobacterium'' species were unified by a unique
synapomorphy In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to have ...
: the presence of the protelomerase gene, ''telA'', which causes all members of the genus to have a linear chromid. By this time, however, the three ''Agrobacterium'' biovars had become defunct; biovar 1 remained with ''Agrobacterium'', biovar 2 was renamed ''
Rhizobium rhizogenes ''Rhizobium rhizogenes'' (formerly ''Agrobacterium rhizogenes'') is a Gram-negative soil bacterium that produces hairy root disease in dicotyledonous plants. ''R. rhizogenes'' induces the formation of proliferative multiple-branched adventitious ...
'', and biovar 3 was renamed '' Allorhizobium vitis''.


Plant pathogen

''Agrobacterium tumefaciens'' causes crown-gall disease in plants. The disease is characterised by a
tumour A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...
-like growth or
gall Galls (from the Latin , 'oak-apple') or ''cecidia'' (from the Greek , anything gushing out) are a kind of swelling growth on the external tissues of plants, fungi, or animals. Plant galls are abnormal outgrowths of plant tissues, similar to be ...
on the infected plant, often at the junction between the root and the shoot. Tumors are incited by the conjugative transfer of a DNA segment (
T-DNA The transfer DNA (abbreviated T-DNA) is the transferred DNA of the tumor-inducing (Ti) plasmid of some species of bacteria such as ''Agrobacterium tumefaciens'' and ''Agrobacterium rhizogenes(actually an Ri plasmid)''. The T-DNA is transferred fr ...
) from the bacterial tumour-inducing (Ti)
plasmid A plasmid is a small, extrachromosomal DNA molecule within a cell that is physically separated from chromosomal DNA and can replicate independently. They are most commonly found as small circular, double-stranded DNA molecules in bacteria; how ...
. The closely related species, ''Agrobacterium rhizogenes'', induces root tumors, and carries the distinct Ri (root-inducing) plasmid. Although the taxonomy of ''Agrobacterium'' is currently under revision it can be generalised that 3 biovars exist within the genus, ''Agrobacterium tumefaciens'', ''Agrobacterium rhizogenes'', and ''Agrobacterium vitis''. Strains within ''Agrobacterium tumefaciens'' and ''Agrobacterium rhizogenes'' are known to be able to harbour either a Ti or Ri-
plasmid A plasmid is a small, extrachromosomal DNA molecule within a cell that is physically separated from chromosomal DNA and can replicate independently. They are most commonly found as small circular, double-stranded DNA molecules in bacteria; how ...
, whilst strains of ''Agrobacterium vitis'', generally restricted to grapevines, can harbour a Ti-plasmid. Non-''Agrobacterium'' strains have been isolated from environmental samples which harbour a Ri-plasmid whilst laboratory studies have shown that non-''Agrobacterium'' strains can also harbour a Ti-plasmid. Some environmental strains of ''Agrobacterium'' possess neither a Ti nor Ri-plasmid. These strains are avirulent. The plasmid T-DNA is integrated semi-randomly into the
genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ge ...
of the host cell, and the tumor morphology genes on the T-DNA are expressed, causing the formation of a gall. The T-DNA carries genes for the biosynthetic enzymes for the production of unusual
amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...
s, typically octopine or
nopaline Nopaline is a chemical compound derived from the amino acids glutamic acid and arginine. It is classified as an opine. Ti plasmids are classified on the basis of the different types of opines they produce. These may be nopaline plasmids, oct ...
. It also carries genes for the biosynthesis of the
plant hormones Plant hormone (or phytohormones) are signal molecules, produced within plants, that occur in extremely low concentrations. Plant hormones control all aspects of plant growth and development, from embryogenesis, the regulation of organ size, pat ...
,
auxin Auxins (plural of auxin ) are a class of plant hormones (or plant-growth regulators) with some morphogen-like characteristics. Auxins play a cardinal role in coordination of many growth and behavioral processes in plant life cycles and are essenti ...
and
cytokinins Cytokinins (CK) are a class of plant hormones that promote cell division, or cytokinesis, in plant roots and shoots. They are involved primarily in cell growth and differentiation, but also affect apical dominance, axillary bud growth, and lea ...
, and for the biosynthesis of
opines Opines are low molecular weight compounds found in plant crown gall tumors or hairy root tumors produced by pathogenic bacteria of the genus ''Agrobacterium'' and ''Rhizobium''. Opine biosynthesis is catalyzed by specific enzymes encoded by gene ...
, providing a carbon and nitrogen source for the bacteria that most other micro-organisms can't use, giving ''Agrobacterium'' a
selective advantage In biology, adaptation has three related meanings. Firstly, it is the dynamic evolutionary process of natural selection that fits organisms to their environment, enhancing their evolutionary fitness. Secondly, it is a state reached by the po ...
. By altering the hormone balance in the plant cell, the division of those cells cannot be controlled by the plant, and tumors form. The ratio of auxin to cytokinin produced by the tumor genes determines the morphology of the tumor (root-like, disorganized or shoot-like).


In humans

Although generally seen as an infection in plants, ''Agrobacterium'' can be responsible for
opportunistic infection An opportunistic infection is an infection caused by pathogens (bacteria, fungi, parasites or viruses) that take advantage of an opportunity not normally available. These opportunities can stem from a variety of sources, such as a weakened immune ...
s in humans with weakened
immune system The immune system is a network of biological processes that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as cancer cells and objects such as wood splinte ...
s, but has not been shown to be a primary pathogen in otherwise healthy individuals. One of the earliest associations of human disease caused by ''Agrobacterium radiobacter'' was reported by Dr. J. R. Cain in Scotland (1988). A later study suggested that ''Agrobacterium'' attaches to and genetically transforms several types of human cells by integrating its T-DNA into the human cell genome. The study was conducted using cultured human tissue and did not draw any conclusions regarding related biological activity in nature.


Uses in biotechnology

The ability of ''Agrobacterium'' to transfer
gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...
s to
plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclud ...
s and fungi is used in
biotechnology Biotechnology is the integration of natural sciences and engineering sciences in order to achieve the application of organisms, cells, parts thereof and molecular analogues for products and services. The term ''biotechnology'' was first used b ...
, in particular,
genetic engineering Genetic engineering, also called genetic modification or genetic manipulation, is the modification and manipulation of an organism's genes using technology. It is a set of technologies used to change the genetic makeup of cells, including t ...
for
plant improvement Plant breeding is the science of changing the traits of plants in order to produce desired characteristics. It has been used to improve the quality of nutrition in products for humans and animals. The goals of plant breeding are to produce cro ...
. Genomes of plants and fungi can be engineered by use of ''Agrobacterium'' for the delivery of sequences hosted in T-DNA binary vectors. A modified Ti or Ri plasmid can be used. The plasmid is 'disarmed' by deletion of the tumor inducing genes; the only essential parts of the T-DNA are its two small (25 base pair) border repeats, at least one of which is needed for plant transformation. The genes to be introduced into the plant are cloned into a plant binary vector that contains the T-DNA region of the disarmed
plasmid A plasmid is a small, extrachromosomal DNA molecule within a cell that is physically separated from chromosomal DNA and can replicate independently. They are most commonly found as small circular, double-stranded DNA molecules in bacteria; how ...
, together with a selectable marker (such as
antibiotic resistance Antimicrobial resistance (AMR) occurs when microbes evolve mechanisms that protect them from the effects of antimicrobials. All classes of microbes can evolve resistance. Fungi evolve antifungal resistance. Viruses evolve antiviral resistance. ...
) to enable selection for plants that have been successfully transformed. Plants are grown on media containing antibiotic following transformation, and those that do not have the T-DNA integrated into their genome will die. An alternative method is
agroinfiltration Agroinfiltration is a method used in plant biology and especially lately in plant biotechnology to induce transient expression of genes in a plant, or isolated leaves from a plant, or even in cultures of plant cells, in order to produce a desired ...
.
Transformation Transformation may refer to: Science and mathematics In biology and medicine * Metamorphosis, the biological process of changing physical form after birth or hatching * Malignant transformation, the process of cells becoming cancerous * Trans ...
with ''Agrobacterium'' can be achieved in multiple ways.
Protoplast Protoplast (), is a biological term coined by Hanstein in 1880 to refer to the entire cell, excluding the cell wall. Protoplasts can be generated by stripping the cell wall from plant, bacterial, or fungal cells by mechanical, chemical or enzy ...
s or alternatively leaf-discs can be incubated with the ''Agrobacterium'' and whole plants regenerated using
plant tissue culture Plant tissue culture is a collection of techniques used to maintain or grow plant cells, tissues or organs under sterile conditions on a nutrient culture medium of known composition. It is widely used to produce clones of a plant in a method known ...
. In
agroinfiltration Agroinfiltration is a method used in plant biology and especially lately in plant biotechnology to induce transient expression of genes in a plant, or isolated leaves from a plant, or even in cultures of plant cells, in order to produce a desired ...
the ''Agrobacterium'' may be injected directly into the leaf tissue of a plant. This method transforms only cells in immediate contact with the bacteria, and results in transient expression of plasmid DNA. Agroinfiltration is commonly used to transform tobacco (''
Nicotiana ''Nicotiana'' () is a genus of herbaceous plants and shrubs in the Family (biology), family Solanaceae, that is Native plant, indigenous to the Americas, Australia, Southwestern Africa and the South Pacific. Various ''Nicotiana'' species, common ...
''). A common transformation protocol for ''
Arabidopsis ''Arabidopsis'' (rockcress) is a genus in the family Brassicaceae. They are small flowering plants related to cabbage and mustard. This genus is of great interest since it contains thale cress (''Arabidopsis thaliana''), one of the model organi ...
'' is the floral dip method:
inflorescence An inflorescence is a group or cluster of flowers arranged on a stem that is composed of a main branch or a complicated arrangement of branches. Morphologically, it is the modified part of the shoot of seed plants where flowers are formed o ...
are dipped in a suspension of ''Agrobacterium'', and the bacterium transforms the
germline In biology and genetics, the germline is the population of a multicellular organism's cells that pass on their genetic material to the progeny (offspring). In other words, they are the cells that form the egg, sperm and the fertilised egg. They ...
cells that make the female
gametes A gamete (; , ultimately ) is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. In species that produce t ...
. The
seed A seed is an embryonic plant enclosed in a protective outer covering, along with a food reserve. The formation of the seed is a part of the process of reproduction in seed plants, the spermatophytes, including the gymnosperm and angiospe ...
s can then be screened for antibiotic resistance (or another marker of interest), and plants that have not integrated the plasmid DNA will die when exposed to the correct condition of antibiotic. ''Agrobacterium'' does not infect all plant species, but there are several other effective techniques for plant transformation including the
gene gun In genetic engineering, a gene gun or biolistic particle delivery system is a device used to deliver exogenous DNA (transgenes), RNA, or protein to cells. By coating particles of a heavy metal with a gene of interest and firing these micro-projec ...
. ''Agrobacterium'' is listed as being the vector of genetic material that was transferred to these USA GMOs: *
Soybean The soybean, soy bean, or soya bean (''Glycine max'') is a species of legume native to East Asia, widely grown for its edible bean, which has numerous uses. Traditional unfermented food uses of soybeans include soy milk, from which tofu an ...
*
Cotton Cotton is a soft, fluffy staple fiber that grows in a boll, or protective case, around the seeds of the cotton plants of the genus ''Gossypium'' in the mallow family Malvaceae. The fiber is almost pure cellulose, and can contain minor perce ...
*
Maize Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn (North American and Australian English), is a cereal grain first domesticated by indigenous peoples in southern Mexico about 10,000 years ago. Th ...
*
Sugar Beet A sugar beet is a plant whose root contains a high concentration of sucrose and which is grown commercially for sugar production. In plant breeding, it is known as the Altissima cultivar group of the common beet (''Beta vulgaris''). Together wi ...
*
Alfalfa Alfalfa () (''Medicago sativa''), also called lucerne, is a perennial flowering plant in the legume family Fabaceae. It is cultivated as an important forage crop in many countries around the world. It is used for grazing, hay, and silage, as w ...
*
Wheat Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeologi ...
* Rapeseed Oil (
Canola Close-up of canola blooms Canola flower Rapeseed oil is one of the oldest known vegetable oils. There are both edible and industrial forms produced from rapeseed, the seed of several cultivars of the plant family Brassicaceae. Historically, i ...
) *
Creeping bentgrass ''Agrostis stolonifera'' (creeping bentgrass, creeping bent, fiorin, spreading bent or carpet bentgrass) is a perennial grass species in the family Poaceae. Description ''Agrostis stolonifera'' is stoloniferous and may form mats or tufts. The ...
(for animal feed) * Rice (
Golden Rice Golden rice is a variety of rice (''Oryza sativa'') produced through genetic engineering to biosynthesize beta-carotene, a precursor of vitamin A, in the edible parts of the rice. It is intended to produce a fortified food to be grown and con ...
) The
transformation Transformation may refer to: Science and mathematics In biology and medicine * Metamorphosis, the biological process of changing physical form after birth or hatching * Malignant transformation, the process of cells becoming cancerous * Trans ...
of fungi using ''Agrobacterium'' is used primarily for research purposes, and follows similar approaches as for plant transformation. The Ti plasmid system is modified to include DNA elements to select for transformed fungal strains, after co-incubation of ''Agrobacterium'' strains carrying these plasmids with fungal species.


Genomics

The sequencing of the
genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ge ...
s of several species of ''Agrobacterium'' has permitted the study of the evolutionary history of these organisms and has provided information on the
gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...
s and systems involved in pathogenesis, biological control and
symbiosis Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasit ...
. One important finding is the possibility that
chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...
s are evolving from
plasmid A plasmid is a small, extrachromosomal DNA molecule within a cell that is physically separated from chromosomal DNA and can replicate independently. They are most commonly found as small circular, double-stranded DNA molecules in bacteria; how ...
s in many of these bacteria. Another discovery is that the diverse chromosomal structures in this group appear to be capable of supporting both symbiotic and pathogenic lifestyles. The availability of the genome sequences of ''Agrobacterium'' species will continue to increase, resulting in substantial insights into the function and evolutionary history of this group of plant-associated microbes.


History

Marc Van Montagu Marc, Baron Van Montagu (born 10 November 1933 in Ghent) is a Belgian molecular biologist. He was full professor and director of the Laboratory of Genetics at the faculty of Sciences at Ghent University (Belgium) and scientific director of the ...
and
Jozef Schell Jozef Stefaan "Jeff", Baron Schell (20 July 1935 – 17 April 2003) was a Belgian molecular biologist. Schell studied zoology and microbiology at the University of Ghent, Belgium. From 1967 to 1995 he worked as a professor at the university. Fro ...
at the
University of Ghent Ghent University ( nl, Universiteit Gent, abbreviated as UGent) is a public research university located in Ghent, Belgium. Established before the state of Belgium itself, the university was founded by the Dutch King William I in 1817, when the ...
(
Belgium Belgium, ; french: Belgique ; german: Belgien officially the Kingdom of Belgium, is a country in Northwestern Europe. The country is bordered by the Netherlands to the north, Germany to the east, Luxembourg to the southeast, France to th ...
) discovered the gene transfer mechanism between ''Agrobacterium'' and plants, which resulted in the development of methods to alter ''Agrobacterium'' into an efficient delivery system for gene engineering in plants. A team of researchers led by Dr Mary-Dell Chilton were the first to demonstrate that the virulence genes could be removed without adversely affecting the ability of ''Agrobacterium'' to insert its own DNA into the plant genome (1983).


See also

*
Agroinfiltration Agroinfiltration is a method used in plant biology and especially lately in plant biotechnology to induce transient expression of genes in a plant, or isolated leaves from a plant, or even in cultures of plant cells, in order to produce a desired ...
*
Marc Van Montagu Marc, Baron Van Montagu (born 10 November 1933 in Ghent) is a Belgian molecular biologist. He was full professor and director of the Laboratory of Genetics at the faculty of Sciences at Ghent University (Belgium) and scientific director of the ...
* ''
Rhizobium rhizogenes ''Rhizobium rhizogenes'' (formerly ''Agrobacterium rhizogenes'') is a Gram-negative soil bacterium that produces hairy root disease in dicotyledonous plants. ''R. rhizogenes'' induces the formation of proliferative multiple-branched adventitious ...
'' (formerly ''Agrobacterium rhizogenes'')


References


Further reading

* **


External links


Current taxonomy of ''Agrobacterium'' species, and new ''Rhizobium'' names


- Plant transformation with ''Agrobacterium''] {{Taxonbar, from=Q2700446 Rhizobiaceae Biotechnology Bacteria genera pl:Agrobacterium tumefaciens