The genome comparisons also turned up some interesting differences between the two B strains. Like identical twins separated at birth, the two B strains have had separate laboratory histories since 1959. One became REL606, a strain used by Richard Lenski at Michigan State University and his collaborators to study long-term evolution in the laboratory. The other became BL21(DE3), a strain developed by Studier and colleagues at Brookhaven Lab to be used as a "factory" for producing proteins for basic research and for medical and industrial use.

"Detailed information about these two strains is useful for future laboratory studies but is also important for companies who are using proteins made from E. coli B strains for medical purposes," Studier said. "They want to know as much as possible about the bacterial strain, including where it came from."

Some detective work was required before the differences between the two B genomes could be understood. Although scientific papers told one story, information in the genome sequences told another, Studier said. The researchers pinpointed the discrepancy to a period in the 1960s, as scientists at different labs shared strains for their research. Apparently, one sample was mislabeled in one of these exchanges. The current detailed genomic analysis uncovered this long-buried mix-up.

Once this mystery was solved, every difference between the two B genome sequences could be understood in terms of the different laboratory manipulations used on the ancestral strains, Studier said. This information provided new insights into the types of changes to the genome caused by standard laboratory treatments, including exposure to chemicals, irradiation with ultraviolet light, and transfer of DNA between genomes.

Source: DOE/Brookhaven National Laboratory