Mutations also appeared in a second, unrelated gene for an enzyme called RNA polymerase. "That was a surprise to almost everybody because RNA polymerase is involved in one of the core processes of any cell," said Palsson. "You wouldn't expect that gene to change because a wide variety of cellular process would be affected; it's like replacing the wiring system in a building when a light bulb burns out. But we repeated the experiment more than 50 times and mutations in the RNA polymerase gene appeared again and again."
The researchers report that mutations in both genes appeared together in several cases after six to eight days in the glycerol-based cultures, and E. coli cells containing both mutated genes grew 150 percent faster than the starting strain of E. coli. To confirm that the mutants were indeed responsible for the faster growth, the researchers substituted the two mutant genes into the original strain and duplicated the faster growth rate. "We expected to find many mutated genes and we thought our results would be very difficult to understand, but neither was the case," said Christopher D. Herring, a co-author of the paper and a former member of Palsson's team who is now a research scientist at Mascoma Corp. in Lebanon, NH.
All the mutants arose in the experiments presumably as the result of naturally occurring errors in copying DNA into daughter cells during cell division. The precise changes in the sequence of DNA subunits were determined with comparative genomic sequencing technology from NimbleGen Systems, and further analyzed with technology from Sequenom Inc., a San Diego-based biotech company.
"This straightforward approach to the study of experimental evolution can be used as a tool for discovery and analysis, and could even be used to d
Source:University of California - San Diego