Tuesday, November 19, 2013

L'Évolution des Bactéries

A 25-year (!) experiment with Escherichia coli bacteria by Richard Lenski and coworkers resulted in a 70% improvement in growth rate or "fitness" in 12 cell lines. 25 years of E. coli growth is equivalent to about a million years of human evolution. Six of the 12 lines developed defects in DNA repair, accumulating mutations at a higher rate than normal. Also, after 3 years of culture, two populations with conspicuous phenotypes evolved in one of the flasks: those making large colonies and those making small ones. Interestingly, neither came to dominate the other, implying two distinct ecological niches even in a high-nutrient culture broth. It's unclear whether such mutations would really be adaptive (contribute to fitness) in the nutrient-limited real world, but it's an example of dogged surrender to a scientific obsession that provides a baseline of data and possibly more. Or possibly not. C'est la science.
BTW, Edison's famous adage that genius is 10% inspiration and 90% perspiration applied to trial-and-error invention. Related to that, yet still different in not having a definitive goal in mind beyond answering a defined and limited question (that then leads to more questions to be answered), this can be amended for the experimental sciences. Genius is 10% inspiration, 20% imagination, 20% perspiration and 49% obsession (which may also include perspiration or not, depending on where one is in the collaborative hierarchy). The extra 1% is sheer brilliance, which is really not that important a factor in the experimental sciences. Or maybe it is. Who knows? C'est la science.

Vol. 342 no. 6160 pp. 790-793 
DOI: 10.1126/science.342.6160.790


The Man Who Bottled Evolution

When most biologists want to understand how evolution unfolds, they look for clues in the fossil record or the natural world. Richard Lenski simply walks across his Michigan State University lab to his freezers. Stored there are bacteria from a 25-year experiment in bacterial evolution. He started with 12 identical populations of Escherichia coli and over time has documented how evolution is roughly reproducible but also endless, even in a stable environment. Fifteen years ago, he almost abandoned it for digital models of evolution, then reconsidered—and was vindicated when his bacteria took one of their most dramatic evolutionary leaps. Now he hopes to keep the experiment going for many, many years more.

1 comment:

  1. There are clearly advantages and disadvantages to prolonged culturing of cells, consistent with the very idea of evolution, everything being in state of flux. There was a big improvement (70%) in the "fitness" or growth rate of all 12 cell lines, and this is good. However all this at big cost as well. Now 50% of the cells had lost their DNA repair mechanisms, hence "accumulating mutations at a higher rate than normal" because something very important to the organism to account for its genetic integrity went missing going from the original culture to the second, then to the third, and to the next one...for 25 years. (cedbiochemistry)