Escherichia coli
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Overview
Escherichia coli is a bacterial species whose strains differ substantially in their genes and behaviour. Some live as part of an intestinal microbial community, while others possess mechanisms associated with disease. A species name therefore cannot determine whether an individual strain is beneficial, neutral or harmful in a particular host and setting.
Laboratory research has made E. coli important for understanding bacterial physiology and genetics. Experiments also investigate competition between commensal and pathogenic strains. A study of ethanolamine use showed that some commensal isolates could grow on this nutrient and compete with a pathogenic strain under specified conditions. The result illustrates how closely related bacteria occupy different ecological roles, while reminding readers that an experimental outcome depends on the organisms and environment tested.
A different experimental setting reveals how this bacterium evolves across many generations. Consuegra and colleagues examined insertion sequences, small mobile DNA elements, in twelve populations of the long-term evolution experiment founded from the common ancestral strain REL606. Their 2021 analysis combined 264 previously sequenced clones, sampled through 50,000 generations, with whole-population sequence data extending through 60,000 generations. The populations evolved in a glucose-limited laboratory environment. A clone records one sampled lineage, whereas population sequencing can follow competing lineages and the rise or disappearance of mutations; neither captures every rare variant.
Insertion sequences can insert into genes or participate in rearrangements between copies, altering gene function and expression. Their evolutionary contribution varied substantially among the experimental populations. Six populations evolved elevated point-mutation rates. Accounting for the time spent in these mutator states, the researchers found that insertion-sequence-related mutations reached fixation at roughly half the rate seen under low point-mutation rates. This is a comparison among the experimental lineages, not a claim that all bacterial mutations occur at a fixed rate or have the same consequences.
The Ara+1 population was especially informative: its IS150 copy number increased eightfold, and it had the lowest fitness trajectory among the experimental populations. Some early IS150 changes had known benefits in the experimental environment, but statistical comparisons associated larger numbers of these changes with poorer later adaptation. The authors proposed that disruptive mutations and the loss of opportunities for later fine-tuning could help explain this constraint. This interpretation does not establish that every insertion is harmful; early benefits and later costs can coexist within the same evolutionary history.
Reporter assays distinguished transposition from recombination in ancestral and evolved clones. IS150 activity subsequently declined, although the elements themselves had not acquired sequence changes explaining the early burst. The responsible regulatory changes remained unidentified. The paper therefore separates measured changes in element activity from hypotheses about feedback, chromosome organization and regulation. Its conclusions concern these asexual laboratory populations; horizontal transfer, which could change the dynamics in natural communities, was not operating in this experiment.
Origins & earliest records
The species was recognised through microbiological investigation of intestinal bacteria, not through a fossil revealing its first emergence. Its modern name and laboratory history should be separated from evolutionary origin. Present-day genome variation records diversification and gene exchange, but this entry does not assign an unsupported geological age to the species.
Evidence & interpretation
Cultured isolates, genome sequences and controlled growth experiments distinguish strain properties. The cited ethanolamine study supplies evidence about two commensal isolates and a specific pathogen under experimental conditions. Its findings should not imply that all E. coli behave identically or that one laboratory competition predicts outcomes in every natural microbiome. The 2021 evolution study combines longitudinal clone and population sequencing with reporter assays; fitness correlations and proposed mechanisms remain distinct from direct experimental measurements.
Selected bibliography
Documented works and useful reading. This is not a list of every appearance.
- 01
Ethanolamine Influences Human Commensal Escherichia coli Growth, Gene Expression, and Competition with Enterohemorrhagic E. coli O157:H7
Selected institutional scientific reading; not a complete bibliography.
- 02
Insertion-sequence-mediated mutations both promote and constrain evolvability during a long-term experiment with bacteria
Nature Communications 12:980, 12 February 2021; DOI 10.1038/s41467-021-21210-7. Complete main Results, Discussion and Methods read, with textual captions; supplementary files, deposited data and code not reanalysed. CC BY 4.0; this profile provides an attributed original summary.
- 03
Escherichia coli K-12 MG1655 sequence and annotations: U00096.1
University of Wisconsin–Madison E.coli Genome Project, U00096.1 historical sequence/annotation account, undated webpage
- 04
The complete genome sequence of Escherichia coli K-12
Science277(5331),1453–1462,5September1997; bibliographic record checked in PubMed9278503
Family, evolution & connections
Selected E. coli and Shigella strains — core-genome branching
Nine strains pruned from Figure 4, plus the study’s E. fergusonii outgroup. Tips represent strains, not separate species.
Scroll sideways to see all branches. With a keyboard, focus the tree and use the arrow keys.
- Study-rooted comparison
- Escherichia fergusonii (outgroup)
- Selected E. coli/Shigella strains
- Selected B2/D branch
- UTI89
- IAI39
- Other selected strains
- UMN026
- Remaining selected strains
- Selected A/B1/Shigella branch
- Sf 301
- Selected A/B1/Sb branch
- MG1655
- IAI1/Sb branch
- IAI1
- Sb 227
- Selected SD1/E branch
- Sd 197
- EDL933
Maximum-likelihood topology from 1,878 core genes; inspected original figure. Branch lengths omitted. Horizontal transfer and recombination are not drawn. Strong concatenated bootstrap support is not uniform agreement among genes. Sampled Shigella strains occupy multiple branches; taxonomic labels are not forced into monophyletic groups.
Taxonomic classification
A hierarchy of classified groups, not a chain of direct ancestors.
- kingdomBacteria
- phylumProteobacteria
- classGammaproteobacteria
- orderEnterobacterales
- familyEnterobacteriaceae
- genusEscherichia
- speciesEscherichia coli
Sampled Shigella strains in Touchon et al. 2009
The core-genome tree nests sampled Shigella strains among E. coli strains on multiple branches. A Shigella label therefore does not define one exclusive evolutionary branch in this dataset. Horizontal transfer and strain sampling remain relevant limitations.
Escherichia fergusonii
The study uses E. fergusonii to root its E. coli/Shigella strain tree. This is a documented role in a sampled analysis, not a claim that this living species is a direct ancestor or necessarily the closest relative under every broader dataset.
Located primary passages
Specific passages supporting details in this entry, grouped by their published witness.
Escherichia coli K-12 MG1655 sequence and annotations: U00096.1
University of Wisconsin–Madison E.coli Genome Project, U00096.1 historical sequence/annotation account, undated webpage
- The research team distinguishes the original1997 MG1655 deposit from later sequence and annotation versions. Its account explains the initial release in400 overlapping GenBank records and tracks gene-boundary, name and product corrections, additions and removals. An annotation therefore represents a dated research product, rather than an immutable inventory applicable to every E.coli strain.
Gene tables and genomes not reanalysed; latest genome record not asserted. The1997 Science paper is a bibliographic lead, not a whole-paper reading.
Insertion-sequence-mediated mutations both promote and constrain evolvability during a long-term experiment with bacteria
2021 published article
- The study combines sequenced clones and population metagenomes from twelve long-term E. coli populations with reporter measurements of insertion-sequence activity. Insertion-sequence mutations contributed differently across lineages. Some early mutations were beneficial, but more such changes were associated with lower later fitness gains. The exceptional IS150 expansion in Ara+1 was followed by reduced activity without corresponding mutations in the element itself. The authors infer contributions from other chromosomal changes but do not identify the exact regulatory mechanism. Hypermutator status and the timing of mutation fixation complicate causal attribution.
No supplementary files, deposited data/code, figure pixels or rerun. Fitness conclusions apply to the studied laboratory conditions; the authors distinguish genomic correlations, measured activity and hypotheses. Horizontal transmission in nature is outside the experiment.
Encyclopedia background
An additional attributed reference, separate from the editorial profile above.
Read the open encyclopedia overview
Escherichia coli ( ESH-ə-RIK-ee-ə KOH-lye) is a gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus Escherichia that is commonly found in the lower intestine of warm-blooded organisms. Most E. coli strains are part of the normal microbiota of the gut, where they constitute about 0.1%, along with other facultative anaerobes. These bacteria are mostly harmless or even beneficial to humans. For example, some strains of E. coli benefit their hosts by producing vitamin K2 or by preventing the colonization of the intestine by harmful pathogenic bacteria. These mutually beneficial relationships between E. coli and humans are a type of mutualistic biological relationship—where both the humans and the E. coli are benefitting each other. E. coli is expelled into the environment within fecal matter. The bacterium grows massively in fresh fecal matter under aerobic conditions for three days, but its numbers decline slowly afterwards.
Some serotypes, such as EPEC and ETEC, are pathogenic, causing serious food poisoning in their hosts. Fecal–oral transmission is the major route through which pathogenic strains of the bacterium cause disease. This transmission method is occasionally responsible for food contamination incidents that prompt product recalls. Cells are able to survive outside the body for a limited amount of time, which makes them potential indicator organisms to test environmental samples for fecal contamination. A growing body of research, though, has examined environmentally persistent E. coli which can survive for many days and grow outside a host.
The bacterium can be grown and cultured easily and inexpensively in a laboratory setting, and has been intensively investigated for over 60 years. E. coli is a chemoheterotroph whose chemically defined medium must include a source of carbon and energy. E. coli is the most widely studied prokaryotic model organism, and an important species in the fields of biotechnology and microbiology, where it has served as the host organism for the majority of work with recombinant DNA. Under favourable conditions, it takes as little as 20 minutes to reproduce.
Text from Wikipedia contributors, “Escherichia coli”. CC BY-SA 4.0. Extracted introduction; formatting changed. Retrieved 5 October 2026. The source article may have changed since retrieval.
References
Sources supporting this profile. Linked pages have their own scope and editorial standards.
- ResearchEthanolamine Influences Human Commensal Escherichia coli Growth, Gene Expression, and Competition with Enterohemorrhagic E. coli O157:H7Research access: 2026-10-05
- ResearchInsertion-sequence-mediated mutations both promote and constrain evolvability during a long-term experiment with bacteriaResearch access: 2026-10-06
Image credits
Reference illustrationEscherichia coli
Image associated with the exact linked encyclopedia article; consult credited file description for its interpretation.
