Escherichia Coli

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Escherichia coli (E. coli) is a very common bacterium that normally inhabits the digestive tract of animals, including humans. It is widespread in the natural world and can also be found in soil and water. It is a member of thebacterial family Enterobacteriaciae, which also includes the bacteria Shigella, Salmonella, and Yersinia, among others. Some of these organisms, including E. coli, can cause serious diseases under certain conditions.

E. coli is important to human health because it is a source of vitamins B12 and K, which it manufactures from undigested food in the large intestine. Unlike many other intestinal bacteria, E. coli can survive and grow in the presence of oxygen (although it can also grow without oxygen), which makes it a useful experimental model organism in the laboratory.

Even though E. coli is a single species of bacteria, many different varieties (called strains) of the species exist. Each has different characteristics, and while some are safe model organisms, others can cause potentially deadly disease. This is the case with E. coli 0157:H7, which is considered a dangerous pathogen which can infect humans. This strain is significantly different from the commonly used laboratory strains, which do not cause disease.

E. coli is the most well-understood bacterium in the world, and is an extremely important model organism in many fields of research, particularly molecular biology, genetics, and biochemistry. It is easy to grow under laboratory conditions, and research strains are very safe to work with. As with many bacteria, E. coli grows quickly, which allows many generations to be studied in a short time. In fact, under ideal conditions, E. coli cells can double in number after only 20 minutes.

Furthermore, a very large number of E. coli bacteria can be grown in a small space—many millions in a drop of broth, for example. These are important characteristics in genetic experiments, which often involve selecting a single bacterial cell from among millions of candidates, then allowing it to reproduce into high numbers again to perform additional experiments.

Many vital techniques, such as molecular cloning and overexpression of cloned genes, were initially developed in E. coli and are still simpler and more effective in the bacterium. Crucial experiments that illuminated the details of fundamental biological processes such as DNA replication, transcription, and translation were performed for the first time or with greatest success in E. coli. The bacterium is still a primary resource in many modern laboratories. Even research efforts that focus on other organisms, including humans or crop plants, often use E. coli extensively as a tool to facilitate cloning and DNA sequencing.

Some of the discoveries made in E. coli have provided an invaluable framework for understanding biological processes in more complex organisms. As mentioned above, many fundamental processes that are shared by all living things are most easily studied in this simple bacterial model. Furthermore,E. coli has served as a model for understanding the biology of other bacteria.

The ways in which E. coli interacts with the human body are in many cases very similar to the ways that other disease-causing organisms act. Therefore, this model organism has been important in the study of humanhealth, and has allowed researchers to ask questions about bacteria in general (for example, how antibiotics stop infections, or how the immune system fights off disease).

Sequencing of the E. coli K-12 strain genome (a popular model strain) was completed in 1997; subsequently, at least two collections of the pathogenic 0157:H7 strain have been completely sequenced. The bacterium has a genome of approximately 4.3 million base pairs of DNA, and carries about 4,400 genes. Interestingly, only about 50 percent of the predicted genes have been described and characterized, a surprisingly low percentage for such a well-understood organism. For this and other reasons, E. coli remains one of the most significant model organisms used today.

Chromosome, Prokaryotic; Eubacteria; Genome; Human Genome Project; Model Organisms; Plasmid.

Madigan, Michael T., John M. Martinko, and Jack Parker. Brock Biology of Micro-organisms, 9th ed. Upper Saddle River, NJ: Prentice Hall, 2000.

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