Why E. coli Is Used for Gene Cloning
A Versatile Microorganism With Incredible Potential
The microorganism Escherichia coli has a long history in the biotechnology industry and is still the microorganism of choice for most gene cloning experiments. Although E. coli is known to the general population for the infectious nature of one particular strain (O157:H7), few people are aware of how versatile and widely used it is in research as a common host for recombinant DNA.
Bacteria make useful tools for genetic research because of their relatively small genome size compared to eukaryotes. E. coli cells only have about 4,400 genes whereas the human genome project has determined that humans contain approximately 30,000 genes. Also, bacteria, including E. coli, live their entire life in a haploid state (having a single set of unpaired chromosomes). As a result, there is no second set of chromosomes to mask the effects of mutations during protein engineering experiments.
Bacteria typically grow much faster than more complex organisms. E. coli grows rapidly at a rate of one generation per 20 minutes under typical growth conditions. This allows for preparation of log-phase (mid-way to maximum density) cultures overnight and genetic experimental results in mere hours instead of several days, months, or years. Faster growth also means better production rates when cultures are used in scaled-up fermentation processes.
E. coli is naturally found in the intestinal tracts of humans and animals where it helps provide nutrients (vitamins K and B12) to its host. There are many different strains of E. coli that may produce toxins or cause varying levels of infection if ingested or allowed to invade other parts of the body. Despite the bad reputation of one particularly toxic strain (O157:H7), E. coli are generally relatively innocuous when handled with reasonable hygiene.
The E. coli genome was the first to be completely sequenced (in 1997). As a result, E. coli is the most highly studied microorganism. Advanced knowledge of its protein expression mechanisms makes it simpler to use for experiments where expression of foreign proteins and selection of recombinants is essential.
Foreign DNA Hosting
Most gene cloning techniques were developed using this bacterium and are still more successful or effective in E. coli than in other microorganisms. As a result, preparation of competent cells (cells that will take up foreign DNA) is not complicated. Transformations with other microorganisms are often less successful.
Ease of Care
Because it grows so well in the human gut, E. coli finds it easy to grow where humans can work. It's most comfortable at body temperature. While 98.6 degrees may be a bit warm for most people, it's easy to maintain that temperature in the laboratory. E. coli lives in the human gut and is happy to consume any type of predigested food. It can also grow both aerobically and anaerobically. Thus, it can multiply in the gut of a human being or animal but is equally happy in a petri dish or flask.