Escherichia coli as an Experimental Organism


Escherichia coli, a gram‐negative gamma proteobacterium, is presently the best‐understood organism. It is a paradigm organism in bacterial physiology and genetics as well as a key tool in molecular genetics in that many genetic manipulations throughout biology involve E. coli. Molecular cloning into one of many E. coli vector plasmids is a standard procedure in most molecular biology and biotechnology laboratories. E. coli is also the workhorse of recombinant protein production since conditions have been found that allow proteins from across biology to be efficiently expressed in and purified from E. coli. Indeed, the bulk of x‐ray crystal structures are performed on proteins that were produced in this bacterium. Finally, a collection of mutant E. coli strains each deleted for a gene nonessential for growth in a rich medium provides a resource to test the functions of genes from other organisms by assaying their ability to replace the function of an E. coli gene.

Key Concepts:

  • E. coli is a preferred host for gene cloning due to the high efficiency of introduction of DNA molecules into cells.

  • E. coli is a preferred host for protein production due to its rapid growth and the ability to express proteins at very high levels.

  • Bacterial conjugation can be used to transfer large DNA fragments from one bacterium to another.

  • E. coli is a preferred host for the study of phage biology due to the detailed knowledge of its nucleic acid and protein biosynthetic pathways.

  • The ability of E. coli to grow on chemically defined media coupled with its extensive genetic toolbox make it a key system in study of bacterial metabolic pathways.

Keywords: conjugation; growth curve; envelope structure; transduction; plasmids; phage; genetics

Figure 1.

A hypothetical growth curve for a culture of E. coli. The four phases of growth are given.

Figure 2.

The cell envelope of E. coli. The dark blue rounded rectangle denotes the inner (cytoplasmic) membrane whereas the red blue rounded rectangle denotes the outer membrane. The thin black rounded rectangle just inside the outer membrane denotes the peptidoglycan layer. In the enlargement of the inner membrane, enlargement the light blue ovals denote the head groups of the phospholipid molecules and the wavy black lines are the fatty acid chains of the phospholipids. The grey shapes denote protein molecules. In the enlargement of the outer membrane structure the designations are the same except that the green boxes denote the lipid A head groups and the chains of differing shapes represent the sugars of the oligosaccharides.

Figure 3.

The donor and recipient cells are denoted by rounded rectangles and the chromosomes by ovals. In the mating pair for simplicity only the chromosome transferred by the donor is shown. The chromosome from which it was copied is not shown. The lower left is an enlargement of the alignment step of homologous recombination in the recipient cell. The X denotes genetic exchange.

Figure 4.

Two E. coli cells undergoing conjugation, one strain has fimbriae. Fimbriae are abundant short filaments that extend from cell surface and play a key role in the attachment of the organism to cell of its animal hosts.



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Cronan, John E(Jul 2014) Escherichia coli as an Experimental Organism. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0002026.pub2]