Lenski's E. Coli: another view (Introduction)

by David Turell , Wednesday, February 24, 2016, 19:46 (3174 days ago) @ David Turell

This very long term E. coli experiment does show that the bacteria can change and mutate to find a new food source, but the results are open to debate about the amount of information used:-http://www.the-scientist.com/?articles.view/articleNo/45423/title/Similar-Data--Different-Conclusions/&utm_campaign=NEWSLETTER_TS_The-Scientist-Daily_2016&utm_source=hs_email&utm_medium=email&utm_content=26586249&_hsenc=p2ANqtz-9NFZR6NdJNBHp7kGDXYsI_PxKDOmK4Bu_hd5BV0dBuBSWGC-l--7cED1T2DpTsEFaO2yabbL9TQTCIQf6Jv7pqkEgyxw&_hsmi=26586249/-"By tweaking certain conditions of a long-running experiment on E. coli, scientists found that some bacteria could be prompted to express a mutant phenotype sooner, without the “generation of new genetic information.” The resulting debate—whether the data support evolutionary theory—is more about semantics than science.
Since 1988, Richard Lenski has been propagating the same 12 cultures of E. coli at Michigan State University, observing how they change over time. These cultures are grown on a low-glucose medium that includes citrate. Every day, members of the Lenski lab transfer the cultures to new media at a dilution of 1:100.-"The team's 2008 finding that some of the bacteria could use citrate as a carbon source under aerobic conditions was considered a game-changer—a potential example of how a new species could emerge (E. coli's inability to metabolize citrate aerobically is one of its defining phenotypic features). Lenski and colleagues attributed the 15-year delay in the appearance of citrate-eating E. coli to the slow accumulation of “potentiating mutations,” genetic changes that provide no discernible advantage at the time but set the stage for future adaptation. Whether a particular culture has a citrate-friendly genetic background depends on its history, the researchers proposed, an idea called historical contingency.-"Now, the authors of a study published this month (February 1) in the Journal of Bacteriology suggest that the delay in the emergence of citrate-eating E. coli may not have been the result of historical contingency, but of experimental conditions that favored non-citrate-eaters. The University of Idaho's Scott Minnich and colleagues have shown that when certain experimental conditions were altered, citrate-eating E. coli mutants (Cit+) appeared much more quickly and displayed similar genetic changes as those seen in bacteria from Lenski's long-term evolution experiment.-***-"Minnich and colleagues grew the LTEE E. coli strain (REL606) in the same glucose- and citrate-containing medium used in the LTEE, but allowed the bacteria to grow for a week before passaging. Under this condition, the team found, Cit+ mutants appeared much faster: as early as 63 days. In a separate experiment, the researchers grew several E. coli strains (excluding REL606) in a medium in which citrate was the only carbon source, to select for citrate-eating bacteria. Cit+ mutants emerged in fewer than 40 days in all but one strain tested, the researchers reported.-***-"The LTEE researchers applaud the experiments conducted by Minnich's team. “The problem . . . is not with the experiments and data. Rather, the problem is that the results are wrapped in interpretations that are, in our view, unscientific and unbecoming,” Blount and Lenski wrote in their blog post.-"“Cit+ mutants exemplify the adaptation capability of microorganisms but as of yet, the LTEE has not substantiated evolution in the broader sense by generation of new genetic information, i.e. a gene with a new function,” Minnich and colleagues wrote in their paper.-“'When natural selection—that is, differential survival and reproduction—favors bacteria whose genomes have mutations that enable them to grow on citrate, those mutations most certainly provide new and useful information to the bacteria,” Lenski and Blount countered in their blog post. “To say there's no new genetic information when a new function has evolved (or even when an existing function has improved) is a red herring that is promulgated by the opponents of evolutionary science.'”-Comment: Case on Lenski's E. coli proving Darwin's evolution is not closed. Whole article is a complex discussion. The issue of new information is central: rearrangement of info or new info?