The bacterium Escherichia coli (E. coli for short) is crucial in modern biotechnology. Scientists use it to store DNA sequences from other organisms, to produce proteins and to test protein function.
E. coli comes from our digestive tract
E. coli lives in the lower intestine of warm-blooded animals, including humans. It’s one of many bacterial species that inhabit our digestive tract in large numbers. In fact, there are more bacterial cells in our digestive tract than there are human cells in our bodies!
There are a large number of E. coli strains (or subtypes) with diverse characteristics. Most are harmless to humans, including the B and K-12 strains that are used routinely for laboratory work. However, some strains are harmful.
Read more about what bacteria are.
Growing E. coli is easy and fast
Scientists first chose to work with E. coli because it was easy and fast to grow in the laboratory.
There are several features of E. coli that make it easy to culture:
- It likes it warm – but not too warm. Because E. coli is a gut bacterium, it grows best at body temperature (37.4ºC). This is an easy temperature for scientists to work with in the laboratory.
- It isn’t fussy about nutrition. E. coli can obtain energy from a wide variety of sources. In its natural environment (the gut), it consumes digested foodstuffs. In a laboratory context, E. coli can be fed easily and cheaply – think chicken soup for bacteria
- It can grow with or without oxygen. In the gut, E. coli grows anaerobically (in the absence of oxygen). However, unlike some anaerobic bacteriaE. coli also grows well in aerobic environments, such as a culture flask in a laboratory.
- It grows fast. Under ideal conditions, individual E. coli cells can double every 20 minutes. At that rate, it would be possible to produce a million E. coli cells from one parent cell within about 7 hours. Fast growth means that experiments involving E. coli can be done quickly, conveniently and cheaply.
E. coli – the first choice for molecular cloning
Because E. coli was used with success in these early experiments and others, it became the bacterium of choice for virtually all molecular cloning. Today, E. coli is used in labs worldwide as a host for foreign DNA sequences and their protein products.
Read these related articles:
- Bacterial DNA – the role of plasmids
- How to add foreign DNA to bacteria
- Restriction enzymes
- Producing foreign proteins in bacteria
The genome of E. coli is well understood
The genome sequence of E. coli (the laboratory strain K-12) was published in 1997. Because of its important role in genetics and biotechnology, it was one of the earliest genome sequences to be completed. Since then, the genomes of numerous other E. coli strains have also been published.
We can understand a lot about how E. coli works by looking at its genome sequence. We know, for instance, that most strains of E. coli have about 4400 genes. We also know the precise DNA sequence of these genes. Using that information, scientists can predict the function of the proteins that are encoded by genes within E. coli.
Because so many E. coli strains have had their genomes sequenced, we can also compare the DNA sequence of genes in different E. coli strains. Comparing gene sequences gives clues to the function of genes, their relative importance and the changes they have undergone over time.
Read this article, Healthy gut bacteria, to get further information about the bacterial populations that inhabit our digestive tract.
Genomes on the Hub
Since the E. coli genome was completed, sequencing genomes has become far faster and cheaper. Today, the genomes of several thousand organisms have been published, including hundreds of plants and animals.
More on genomes:
The animation How enzymes work gives a clear explanation of how enzymes work to catalyse biological chemical reactions.
The Infection Inspection citizen science project is using E. coli to help develop a faster test for antibiotic resistance. They need your observation skills to help identify bacteria that have been impacted by antibiotics.
Learn more about the role of E. coli in the first recombinant DNA experiments by exploring this interactive from the DNA Learning Centre.
Watch these videos from the National Genome Research Institute for a step-by-step guide to how a genome is sequenced.