Techniques in Molecular Biology – Basic E. Coli Information for Molecular Biology

Common E. coli strains used in molecular biology. Most Escherichia coli (E. coli) strains used by most molecular biology applications are rod-shaped bacteria named after Dr. Theodor Escherich, who first described these intestinal gram-negative bacteria. There are two parent strains for the hundreds of E. coli commonly used. These are K-12 and B strain bacteria. K-12, isolated from feces of a diphtheria patient lead to DH5a while the B strain eventually became BL21 strain after passing through the laboratories of several scientists. The E. coli strains are commonly used because they easily grow on solid and liquid medium at a fairly high doubling rate of 20-30 min. An overnight culture from an isolated colony can yield about 2 billion cells per milliliter in liquid culture. From these two strains (there are other less commonly used strains) many new, related bacterial strains have been generated by mutating genomic genes and or adding additional new genes.