A group of researchers from Michigan State University (USA) has carried out a patient experiment lasting no less than 25 years, throughout which they have been analyzedmore than 50,000 generations of the bacteriaEscherichia coli.As a result, the team has been able to identify mutations in the species that have led to the development of a new function. In other words: the experiment has made it possible to ‘see’ directly the famous evolution by small changes that Darwin spoke of in the 19th century.
According to this theory,mutations in the genetic code of a species lead to the appearance of new functionsor characters. These changes happen gradually, and it takes many, many generations for them to manifest. Therefore, on a human scale, evolution is very difficult to observe, since we do not live long enough to do so. To overcome this problem, the team of researchers selected a bacterium, whose life span is short and allows thousands of generations to be studied in a relatively short time.
Over 25 years, researchers have followed twelve populations ofEscherichia coli over some 50,000 generations. Each day they extracted a subsample from each population and frozen it, so that when scientists looked at a new function, they could ‘go back’ in time and reconstruct the facts by analyzing previous generations.
Specifically, in the 33,000th generation the team observed that the species had acquired theability to digest citrate in the presence of oxygen. The scientists conducted a genomic analysis of previous generations, the results of which are published in the journalNature, and they managed to reconstruct the steps that led to the acquisition of the new skill. “It was not a typical mutation,” explains Richard E. Lenski, director of the research. “Part of the genome has been copied and the pieces of DNA were stitched together in a new way. One fragment encodes a protein that allows citrate to enter the cell, and the other allows the activation of said protein.”
Although other works have found some of these gradual changes, this is the longest that has been carried out to date, and the first that has allowed the reconstruction of all the steps prior to it.
