Until generation 20, 000, the development of the bacteria was very even, the researchers discovered: The speed with which changes in the genome? so-called mutations? accumulated, remained virtually constant during this time. However, as expected, this was not accompanied by a constant improvement in the fitness of the bacteria: at first, a large part of the mutations seems to have had a positive effect on the survival of the microbes, because they grew measurably faster than the original population. Then, however, this rate of adaptation subsided, although the mutation rate remained the same.
After about 26, 000 generations, there must have been a mutation that affected the DNA metabolism. As a consequence, the mutation rate increased rapidly. For example, while there were 45 detectable mutations after 20, 000 generations, it was already 653 after 40, 000 generations, and the genome at that time was 1.2 percent shorter than that of the original bacteria. However, most of these changes do not seem to have had a very positive or very negative impact on the viability of the bacteria, the researchers write. Some of the mutational variants that occurred in the laboratory cultures are found, or similar, in pathogenic bacteria. Laboratory evolution could therefore help to better understand and effectively counter these potentially dangerous changes.Richard Lenski (Michigan State University, East Lansing) et al .: Nature, online pre-release, doi: 10.1038 / nature08480 ddp / science.de? Ilka Lehnen-Beyel advertisement