FIGURE 1 

E. coli K-12 pedigree. The relationships of E. coli K-12 MG1655 and W3110 with wild-type E. coli K-12 (EMG2 or WG1) have been described (Bachmann, 1972, 1996). Wild-type K-12 was cured of phage to make W1485 prior to 1954 (Step 1), which in turn was cured of the F⁺ factor to make W2637 (Step 2), from which W3110 was selected for a strongly galactose-fermenting strain in 1956 (Step 3). More recently, W1485 was cured of the F⁺ factor to make MG1655 (Guyer et al, 1981). E. coli K-12 EMG2, W1485, W2637, and W3110 have the same rpoS396(Am) allele (codon 33, TAG (Am); Rod et al, 1988; Atlung et al, 2002; KA Datsenko and BL Wanner, unpublished data), while MG1655 has the pseudorevertant Q33 allele (Atlung et al, 2002).