Escherichia coli (molecular biology)
Escherichia coli is a gammaproteobacterium
Gammaproteobacteria is a class of several medically, ecologically and scientifically important groups of bacteria, such as the Enterobacteriaceae , Vibrionaceae and Pseudomonadaceae. An exceeding number of important pathogens belongs to this class, e.g...

 commonly found in the lower intestine
Gastrointestinal tract
The human gastrointestinal tract refers to the stomach and intestine, and sometimes to all the structures from the mouth to the anus. ....

 of warm-blooded
The term warm-blooded is a colloquial term to describe animal species which have a relatively higher blood temperature, and maintain thermal homeostasis primarily through internal metabolic processes...

 organisms (endotherms) and the descendants of two isolates (K-12 and B strain) are used routinely in molecular biology as both a tool and a model organism.

Diversity of Escherichia coli

Escherichia coli is one of the most diverse bacterial species with several pathogenic strains with different symptoms and with only 20% of the genome is common to all strains. Furthermore, from the evolutionary point of view, the members of genus Shigella
Shigella is a genus of Gram-negative, nonspore forming, non-motile, rod-shaped bacteria closely related to Escherichia coli and Salmonella. The causative agent of human shigellosis, Shigella causes disease in primates, but not in other mammals. It is only naturally found in humans and apes. During...

 (dysenteriae, flexneri, boydii, sonnei) are actually E. coli strains "in disguise"
Taxa in disguise
In bacteriology a taxon in disguise is a species, genus or higher unit of biological classification whose evolutionary history reveals has evolved from another unit of similar or lower rank, making the parent unit paraphyletic...

 (i.e. E.coli is paraphyletic to the genus).


In 1885, Theodor Escherich
Theodor Escherich
Theodor Escherich was a German-Austrian pediatrician and a professor at universities in Graz, and Vienna...

, a German pediatrician, first discovered this species in the feces of healthly individuals and called it Bacterium coli commune due to the fact it is found in the colon and early classifications of Prokaryotes placed these in a handful of genera based on their shape and motility (at that time Ernst Haeckel
Ernst Haeckel
The "European War" became known as "The Great War", and it was not until 1920, in the book "The First World War 1914-1918" by Charles à Court Repington, that the term "First World War" was used as the official name for the conflict.-Research:...

's classification of Bacteria in the kingdom Monera
Monera is a superseded kingdom that contains unicellular organisms without a nucleus , such as bacteria....

 was in place).

Following a revision of Bacteria it was reclassified as Bacillus coli by Migula in 1895 and later reclassified as Escherichia coli

Due to its ease of culture and fast doubling it was used in the early microbiology experiments, however bacteria were considered primitive and pre-cellular and received little attention before 1944, when Avery, Macleod and McCarty demonstrated that DNA was the genetic material using Salmonella typhimurium, following which Escherichia coli was used for linkage mapping studies

Escherich's isolate

The first isolate of Escherich was deposited in NCTC in 1920 by the Lister Institute in London (NCTC 86


A strain was isolated from a stool sample of a patient convalescent from diphtheria and was labelled K-12 (not an antigen) in 1922 at Stanford University. This isolate was used in 1940s by Charles E. Clifton to study nitrogen metabolism who deposited it in ATCC (strain ATCC 10798) and lent it to Edward Tatum for his tryptophan biosynthesis experiments, despite its idiosyncrasies due to the F+ λ+ phenotype
In the course of the passages it lost its O antigen and in 1953 was cured first of its lambda phage (strain W1485 by UV by Joshua Lederber and colleagues) and then in 1985 of the F plasmid by acridine orange curing by G Plunkett, M. Berlyn, M. Guyer MG1655). Strains derived from MG1655 include DH1, parent of DH5α and in turn of DH10β (rebranded as TOP10 by Invitrogen).
An alternative lineage from W1485 is that of W2637 (which contains an inversion rrnD-rrnE), which in turn resulted in W3110.
Due to the lack of specific record-keeping, the "pedigree" of strains was not available and had to be inferred by consulting lab-book and records in order to set up the Harvard Stock Centre. The different strains have been derived through treating E.coli K-12 with agents such as nitrogen mustard, ultra-violet radiation, X-ray etc. A full list of Escherichia Coli K-12 strain derivatives and their individual construction, genotypes, phenotypes, plasmids and phage information can be viewed at Ecoliwiki.

B strain

A second common laboratory strain is the B strain, whose history is less straightforward and the first naming of the strain as E. coli B was by Delbrück and Luria in 1942 in their study of bacteriophages T1 and T7 The original E. coli B strain, known then as Bacillus coli, originated from Félix d'Herelle from the Institut Pasteur in
Paris around 1918 who studied bacteriophages, who claimed that it originated from Collection of the Institut Pasteur, but no strains of that period exist. The strain of d'Herelle was passed to Jules Bordet, Director of the Institut Pasteur du Brabant in Bruxelles and his student André Gratia The former passed the strain to Ann Kuttner ("the Bact. coli obtained
from Dr. Bordet") and in turn to Eugène Wollman (B. coli Bordet), whose son deposited it in 1963 (CIP
63.70) as "strain BAM" (B American), while André Gratia passed the strain to Martha Wollstein, a researcher at Rockefeller, who refers to the strain as "Brussels strain of Bacillus coli" in 1921, who in turn passed it to Jacques Bronfenbrenner (B. coli P.C.), who passed it to Delbrück and Luria.
This strain gave rise to several other strains, such as REL606 and B21.

Role in biotechnology

Because of its long history of laboratory culture and ease of manipulation, E. coli also plays an important role in modern biological engineering
Biological engineering
Biological engineering, biotechnological engineering or bioengineering is the application of concepts and methods of biology to solve problems in life sciences, using engineering's own analytical and synthetic methodologies and also its traditional...

 and industrial microbiology
Industrial microbiology
Industrial microbiology or microbial biotechnology encompasses the use of microorganisms in the manufacture of food or industrial products. The use of microorganisms for the production of food, either human or animal, is often considered a branch of food microbiology...

. The work of Stanley Norman Cohen
Stanley Norman Cohen
Stanley Norman Cohen is an American geneticist.Cohen is a graduate of Rutgers University, and received his doctoral degree from the University of Pennsylvania School of Medicine in 1960...

 and Herbert Boyer
Herbert Boyer
Herbert W. Boyer is a recipient of the 1990 National Medal of Science, co-recipient of the 1996 Lemelson-MIT Prize, and a co-founder of Genentech. He served as Vice President of Genentech from 1976 through his retirement in 1991....

 in E. coli, using plasmid
In microbiology and genetics, a plasmid is a DNA molecule that is separate from, and can replicate independently of, the chromosomal DNA. They are double-stranded and, in many cases, circular...

s and restriction enzyme
Restriction enzyme
A Restriction Enzyme is an enzyme that cuts double-stranded DNA at specific recognition nucleotide sequences known as restriction sites. Such enzymes, found in bacteria and archaea, are thought to have evolved to provide a defense mechanism against invading viruses...

s to create recombinant DNA
Recombinant DNA
Recombinant DNA molecules are DNA sequences that result from the use of laboratory methods to bring together genetic material from multiple sources, creating sequences that would not otherwise be found in biological organisms...

, became a foundation of biotechnology.

Considered a very versatile host for the production of heterologous
In medicine a heterologous transplant means 'between species' or 'from one species to another'.In cell biology and protein biochemistry, heterologous expression means that a protein is experimentally put into a cell that does not normally make that protein...

Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

s, researchers can introduce genes into the microbes using plasmids, allowing for the mass production of proteins in industrial fermentation
Industrial fermentation
Industrial fermentation is the intentional use of fermentation by microorganisms such as bacteria and fungi to make products useful to humans. Fermented products have applications as food as well as in general industry.- Food fermentation :...

 processes. Genetic systems have also been developed which allow the production of recombinant proteins using E. coli. One of the first useful applications of recombinant DNA
Recombinant DNA
Recombinant DNA molecules are DNA sequences that result from the use of laboratory methods to bring together genetic material from multiple sources, creating sequences that would not otherwise be found in biological organisms...

 technology was the manipulation of E. coli to produce human insulin
Insulin is a hormone central to regulating carbohydrate and fat metabolism in the body. Insulin causes cells in the liver, muscle, and fat tissue to take up glucose from the blood, storing it as glycogen in the liver and muscle....

. Modified E. coli have been used in vaccine
A vaccine is a biological preparation that improves immunity to a particular disease. A vaccine typically contains an agent that resembles a disease-causing microorganism, and is often made from weakened or killed forms of the microbe or its toxins...

 development, bioremediation
Bioremediation is the use of microorganism metabolism to remove pollutants. Technologies can be generally classified as in situ or ex situ. In situ bioremediation involves treating the contaminated material at the site, while ex situ involves the removal of the contaminated material to be treated...

, and production of immobilised enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

s. E. coli cannot, however, be used to produce some of the more large, complex proteins which contain multiple disulfide bond
Disulfide bond
In chemistry, a disulfide bond is a covalent bond, usually derived by the coupling of two thiol groups. The linkage is also called an SS-bond or disulfide bridge. The overall connectivity is therefore R-S-S-R. The terminology is widely used in biochemistry...

s and, in particular, unpaired thiol
In organic chemistry, a thiol is an organosulfur compound that contains a carbon-bonded sulfhydryl group...

s, or proteins that also require post-translational modification for activity.

Studies are also being performed into programming E. coli to potentially solve complicated mathematics problems such as the Hamiltonian path problem
Hamiltonian path problem
In the mathematical field of graph theory the Hamiltonian path problem and the Hamiltonian cycle problem are problems of determining whether a Hamiltonian path or a Hamiltonian cycle exists in a given graph . Both problems are NP-complete...


Model organism

E. coli is frequently used as a model organism
Model organism
A model organism is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the organism model will provide insight into the workings of other organisms. Model organisms are in vivo models and are widely used to...

 in microbiology
Microbiology is the study of microorganisms, which are defined as any microscopic organism that comprises either a single cell , cell clusters or no cell at all . This includes eukaryotes, such as fungi and protists, and prokaryotes...

 studies. Cultivated strains (e.g. E. coli K12) are well-adapted to the laboratory environment, and, unlike wild type
Wild type
Wild type refers to the phenotype of the typical form of a species as it occurs in nature. Originally, the wild type was conceptualized as a product of the standard, "normal" allele at a locus, in contrast to that produced by a non-standard, "mutant" allele...

 strains, have lost their ability to thrive in the intestine. Many lab strains lose their ability to form biofilm
A biofilm is an aggregate of microorganisms in which cells adhere to each other on a surface. These adherent cells are frequently embedded within a self-produced matrix of extracellular polymeric substance...

s. These features protect wild type strains from antibodies
An antibody, also known as an immunoglobulin, is a large Y-shaped protein used by the immune system to identify and neutralize foreign objects such as bacteria and viruses. The antibody recognizes a unique part of the foreign target, termed an antigen...

 and other chemical attacks, but require a large expenditure of energy and material resources.

In 1946, Joshua Lederberg
Joshua Lederberg
Joshua Lederberg ForMemRS was an American molecular biologist known for his work in microbial genetics, artificial intelligence, and the United States space program. He was just 33 years old when he won the 1958 Nobel Prize in Physiology or Medicine for discovering that bacteria can mate and...

 and Edward Tatum first described the phenomenon known as bacterial conjugation
Bacterial conjugation
Bacterial conjugation is the transfer of genetic material between bacterial cells by direct cell-to-cell contact or by a bridge-like connection between two cells...

 using E. coli as a model bacterium, and it remains the primary model to study conjugation. E. coli was an integral part of the first experiments to understand phage
A bacteriophage is any one of a number of viruses that infect bacteria. They do this by injecting genetic material, which they carry enclosed in an outer protein capsid...

 genetics, and early researchers, such as Seymour Benzer
Seymour Benzer
Seymour Benzer was an American physicist, molecular biologist and behavioral geneticist. His career began during the molecular biology revolution of the 1950s, and he eventually rose to prominence in the fields of molecular and behavioral genetics. He led a productive genetics research lab both at...

, used E. coli and phage T4 to understand the topography of gene structure. Prior to Benzer's research, it was not known whether the gene was a linear structure, or if it had a branching pattern.

E. coli was one of the first organisms to have its genome sequenced; the complete genome of E. coli K-12 was published by Science in 1997.

Lenski's long term evolution experiment

The long-term evolution experiments using E. coli, begun by Richard Lenski
Richard Lenski
Richard E. Lenski is an American evolutionary biologist. He is the son of sociologist Gerhard Lenski. He earned his BA from Oberlin College in 1976, and his PhD from the University of North Carolina in 1982...

 in 1988, have allowed direct observation of major evolutionary shifts in the laboratory. In this experiment, one population of E. coli unexpectedly evolved the ability to aerobically metabolize citrate
A citrate can refer either to the conjugate base of citric acid, , or to the esters of citric acid. An example of the former, a salt is trisodium citrate; an ester is triethyl citrate.-Other citric acid ions:...

. This capacity is extremely rare in E. coli. As the inability to grow aerobically is normally used as a diagnostic criterion with which to differentiate E. coli from other, closely related bacteria such as Salmonella
Salmonella is a genus of rod-shaped, Gram-negative, non-spore-forming, predominantly motile enterobacteria with diameters around 0.7 to 1.5 µm, lengths from 2 to 5 µm, and flagella which grade in all directions . They are chemoorganotrophs, obtaining their energy from oxidation and reduction...

, this innovation may mark a speciation
Speciation is the evolutionary process by which new biological species arise. The biologist Orator F. Cook seems to have been the first to coin the term 'speciation' for the splitting of lineages or 'cladogenesis,' as opposed to 'anagenesis' or 'phyletic evolution' occurring within lineages...

event observed in the lab.
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