page_title: E. coli long-term evolution experiment
hierarchical_section_title: E. coli long-term evolution experiment
caption_attribution_description: English: Photograph of Richard Lenski's long-term evolution experiment with E. coli taken on 25 June 2008. Each flask harbors one of the 12 evolving populations. The photo was taken about 24 h after the cultures were serially transferred, hence they are at stationary phase. The populations grow in DM25 medium, which contains a relatively low glucose concentration so that the culture is not very turbid. However, one population, designated Ara-3, evolved to use the citrate that is also present in the medium. It has a much greater density of cells than the others, and it is therefore much more turbid, owing to the high concentration of citrate in the medium supporting greater cell growth.Русский: Колбы с 12 популяциями E. coli, участвующими в долговременном эколюционном эксперименте Ричарда Ленски, 25 июня 2008. Культуры перенесены в свежую питательную среду 24 часа назад и уже находятся в стационарной фазе (т.е. глюкоза уже кончилась, деление клеток прекратилось). Популяция взращиваются в питательной среде DM25, которая содержит относительно небольшое количество глюкозы, так что плотность культур не очень велика. Однако одна из популяций, обозначенная как Ara-3, приноровилась питаться цитратом, который тоже входит в состав питательной среды. Это позволило ей достигнуть большей плотности (жидкость в колбе А-3 заметно более мутная, чем в других колбах).
context_page_description: The E. coli long-term evolution experiment is an ongoing study in experimental evolution led by Richard Lenski that has been tracking genetic changes in 12 initially identical populations of asexual Escherichia coli bacteria since 24 February 1988. The populations reached the milestone of 50,000 generations in February 2010. Lenski performed the 10,000th transfer of the experiment on March 13, 2017. The populations reached 73,500 generations in early 2020, shortly before the being frozen because of the COVID-19 pandemic.
  Over the course of the experiment, Lenski and his colleagues have reported a wide array of phenotypic and genotypic changes in the evolving populations. These have included changes that have occurred in all 12 populations and others that have only appeared in one or a few populations. For example, all 12 populations showed a similar pattern of rapid improvement in fitness that decelerated over time, faster growth rates, and increased cell size. Half of the populations have evolved defects in DNA repair that have caused mutator phenotypes marked by elevated mutation rates.
context_section_description: The E. coli long-term evolution experiment (LTEE) is an ongoing study in experimental evolution led by Richard Lenski that has been tracking genetic changes in 12 initially identical populations of asexual Escherichia coli bacteria since 24 February 1988. The populations reached the milestone of 50,000 generations in February 2010. Lenski performed the 10,000th transfer of the experiment on March 13, 2017. The populations reached 73,500 generations in early 2020, shortly before the being frozen because of the COVID-19 pandemic.
  Over the course of the experiment, Lenski and his colleagues have reported a wide array of phenotypic and genotypic changes in the evolving populations. These have included changes that have occurred in all 12 populations and others that have only appeared in one or a few populations. For example, all 12 populations showed a similar pattern of rapid improvement in fitness that decelerated over time, faster growth rates, and increased cell size. Half of the populations have evolved defects in DNA repair that have caused mutator phenotypes marked by elevated mutation rates. The most striking adaptation reported so far is the evolution of aerobic growth on citrate, which is unusual in E. coli, in one population at some point between generations 31,000 and 31,500.
  Lenski took the decision to pause the experiment on 9 March 2020 when his lab temporarily closed as a precaution against the spread of COVID19. All of the long-term lines have been placed into ultra-low-temperature storage until such time as they can be defrosted for the experiment to continue.
  On May 4, 2020, Lenski announced a 5-year renewal of the grant through the National Science Foundation's Long-Term Research in Environmental Biology (LTREB) Program that supports the LTEE. He also announced that the experiment would be transferred to the supervision of Dr. Jeffrey E. Barrick, an associate professor of Molecular Biosciences at The University of Texas at Austin, within the next 5 years. Dr. Barrick had previously been a postdoctoral researcher with Dr. Lenski, and has been a major contributor to research based upon the LTEE.
caption: The 12 E. coli LTEE populations on June 25, 2008.[1]
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