Escherichia coli as a model organism
/ esh-uh-RIK-ee-uh KOH-lye, often just 'E. coli' /
If molecular biology has a laboratory mascot, it is Escherichia coli, a rod-shaped bacterium that normally lives harmlessly in the human gut. Cheap to grow, doubling about every twenty minutes, and easy to manipulate, it became the organism on which much of the foundational machinery of life was first worked out. For decades 'what is true for E. coli is true for the elephant', in Jacques Monod's famous phrase, was the working faith of the field.
Its virtues are practical. A single bacterium grown overnight yields billions of identical descendants, so experiments are fast and statistically powerful. Its genome is small, around 4.6 million base pairs and a few thousand genes, and fully sequenced. Best of all, it readily takes up foreign DNA, so researchers can put a chosen gene on a small circular DNA called a plasmid, push it into E. coli, and let the bacteria copy and even build the protein for them. This is the everyday workhorse of recombinant DNA: most cloning, much protein production, and a great deal of teaching all run through E. coli.
The trade-off is exactly what makes it convenient: it is a prokaryote, so it lacks a nucleus, introns, and the elaborate chromatin and RNA processing of our own cells, and lessons from it do not always carry straight over to eukaryotes. Even so, the genetic code, the basics of transcription and translation, the lac operon model of gene regulation, and the first recombinant DNA were all first understood in E. coli, which is why no tour of molecular biology can skip it.
Human insulin for diabetics is made by inserting the human insulin gene into E. coli on a plasmid and letting vats of the bacteria churn out the protein — one of the first and most useful triumphs of recombinant DNA.
E. coli is a living factory for proteins we cannot easily make any other way.
The lab strains of E. coli are tame and harmless; they are not the rare disease-causing strains (like O157:H7) you hear about in food poisoning. The species is mostly a benign gut resident.