Arguably one of the most studied organisms in biology, E. coli is a bacterium found in the lower intestines of mammals. Studies of E.coli DNA have helped scientists to develop sequencing technology, and provide a base from which to study the genes of other organisms.
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What is Escherichia Coli?
Escherichia coli, to give the bacterium its full name, gets a bad rap. This is largely due to the small number of strains that can cause food poisoning, but most strains are harmless and indeed some are beneficial. They are good news when they produce vitamin K and when they prevent pathogens from taking up residence inside our guts. The bacterium was discovered in 1885 by German paediatrician Theodor Escherich.
The K-12 strain, which is not pathogenic, is probably the hardest working bacterium in biology. It is a favourite of researchers working in biochemistry, genetics, and physiology, and is used to produce human insulin and other therapeutics.
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E. Coli Bacteria Facts
In 1997 researchers from the Laboratory of Genetics at the University of Wisconsin-Madison revealed the fruits of their extensive work on E.Coli DNA. They published its complete genome sequence which consists of some 4, 639, 221 base pairs containing 4,403 genes.
The scientists also compared each E.coli gene with the gene of every other organism that had been sequenced at the time. The comparison confirmed a widely held belief that many genes are common in nature; there was also some unique E. Coli genes. Knowledge gleaned from this is useful because it may tell scientists how the bacterium evolved and the minimum number of crucial genes it needs to survive.
Other E.coli strains have subsequently been sequenced;
E.coli 0157:H7 - causes haemorrhagic colitis, haemolytic uremic syndrome - 5.4 million base pairs
Uropathogenic E.coli - causes cystitis, pylonephritis - 5.2 million base pairs.
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E. Coli 'Sex'
E. coli DNA has another big claim to fame. It was the model organism in which Joshua Lederberg and Edward Tatum found the phenomenon of bacterial conjugation, or 'bacterial sex' as it is sometimes referred to: "Analysis of mixed culture of nutritional mutants has revealed the presence of new types which strongly suggest the occurrence of a sexual process in the bacterium Escherichia coli." (Nature, Vol. 8, pg 558, October 19, 1946).
Conjugation is not actually a sexual process as no zygote is formed, but there is the transfer of genetic material between bacteria via cell -to-cell contact.
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E. Coli DNA Manipulation
E.coli's long history as a favoured lab tool, and the ease with which it can be manipulated helped to kick start the biotechnology revolution. An interesting E.coli fact is that In 1973 it became the world's first genetically engineered organism. The credit for the work goes to Stanley Cohen and Herb Boyer who showed the world that it was possible to move genes from one organism to another.
Prior to their collaboration Cohen had demonstrated that E. coli could take up a plasmid that conferred resistance to the antibiotic tetracycline. Then with Boyer the scientists were able to cut this plasmid in a precise location and splice in another antibiotic resistant gene, and the vector was taken up by E.coli and the genes expressed. And so the new field of genetic engineering was born.