Study of Escherichia Erlemeyerii

Phenotypic and Genomic Evolution during a 20-year Experiment with E. coli

Richard Lenski
Evolutionary Biologist
Michigan State University

picture-2[image from R. Lenski lab website]

April 30, 2009 lecture at the Plant and Molecular Biology Department, University of California at Berkeley

[my notes]

Evolution in action
–    Darwin introduced artificial selection
–    Ex: Pigeon breeding
–    Ex: antibiotic resistance of microbes, influenza isolated over year (PNAS 1997)
–    Ex: designed experiment in lab

E. coli 21 yr study started 1988, now +48K passages
– No plasmids or viruses
– clonal poulation
– ancestral genotypes frozen at -80C
– variation independently arises, and not variation in a population
– competition of ancestor vs decendant organisms

12 replicate populations all started from E. coli B
– every day .1 ml is transferred into 10 ml of fresh media
– will they all adapt the same wa

The bacterium E. coli is routinely genetically...
Image via Wikipedia

Phenotypes

-he worked from phenotypes to genotypes to ecology
–    after 2K generations, progeny grew faster than ancestors, with 10% jumps in fitness
–    after 20K generations, the rate of improvement shoulders and approaches a maximum
–    similar trends for increasing cell size as for growth rate

Luria-Delbruck style fluctuation test
–    some populations increased the rate of mutations, but not all
–    narrowing catabolic niche (ability to use var. carbon sources), but not wholesale, just by percents
–    parallel phenotypic evolution in samples
–    phage convergence also seen

Genomics
–    molecular archeology for use of E. coli
–    after 20K generations, 29 point mutations, 15 indels, 1 inverstion (45 total mutaions)
–    linear accumulations of mutations… seems like neutral evolution? But fitness evolution (via phenotypic data) is going on faster
–    most found mutations fall along the line of descent, meaning that they aren’t from individuals different than that of the population

Charles Darwin's 1837 sketch, his first diagra...
Image via Wikipedia

–    off-line mutations were off the line of descent and later substituted
–    mutations substituted by positive selection
–    convergent evolution in genes, and not classic molecular drift
–    selectively driven molecular clock

1 of 12 cultures starts using citrate instead of glucose
– used 454 sequencing to find which gene was mutated

– tried to make a mutation by plating several trillion E. coli on citrate only plates, with no mutations in the first 20K generations, but from 20-30K      he found a handful of mutants that can live on citrate only (E. coli typically only likes glucose, and can’t eat citrate)

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One response to “Study of Escherichia Erlemeyerii

  1. Wow, I was a bio major in college and I actually remember some of this stuff! I love it, evolution was one of the most debated topics in my 400 level classes and I loved it!

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