E. coli – the biotech bacterium

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

Since the birth of molecular cloning, E. coli has been used as a host for introduced DNA sequences. In 1973, Herbert Boyer and Stanley Cohen showed for the first time that two short pieces of bacterial DNA could be ‘cut and pasted’ together and returned to E. coli. They went on to show that DNA from other species, such as frogs, could also be introduced to E. coli.

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.