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Evolution in Action

The Power of Mutation in E. coli


Merle K. Heidemann (rr)
College of Natural Science, Emeritus
Michigan State University
Peter J.T. White
Lyman Briggs College
Michigan State University
James J. Smith
Lyman Briggs College
Michigan State University


This case study is based on Dr. Richard Lenski’s ongoing studies of evolution in E. coli. Students are introduced to prokaryotic biology and to Lenski’s studies based on serial broth cultures of E. coli, which have been monitored for genotypic and phenotypic changes for over 25 years. One subculture evolved the ability to use citrate as food source under conditions where it previously could not. Students explore the cell biology, molecular genetics and ecology of this system by engaging in modules that tie into one another using evolution as an overarching theme. The modules can be used in any order across the biology curriculum or can be used to revisit and/or summarize previously learned topics. This integrative approach employs both problem-based learning techniques and directed questions as students engage in the modules. The case study is appropriate for an introductory biology course, an AP or Honor’s high school biology course or an upper level course in evolution. The research phase of problem-based learning is supported by a series of PowerPoint slides that can be downloaded, edited and used according to instructors’ needs.


  • Understand that the study of evolution requires learning across the biological sciences curriculum and provide relevant examples.
  • Describe fundamental bacterial structure and function, particularly related to metabolism; describe the system for the E. coli LTEE.
  • Explain citric acid cycle function, inputs and outputs; explain changes in protein function when E. coli evolved to utilize citrate in aerobic conditions.
  • Explain the changes in the genetic material, DNA, that permitted E. coli to utilize citrate in aerobic conditions in addition to anaerobic conditions.
  • Use principles of ecology to explain the coexistence of two different E. coli strains in a single culture.


Evolution; operon; molecular genetics; gene expression; bacterial ecology; citrate metabolism; citric acid cycle; transporter proteins; cit operon; repressors; E. coli metabolism; DNA duplication

Topical Areas


Educational Level

High school, Undergraduate lower division, Undergraduate upper division


PDF, PowerPoint

Type / Methods

Discussion, Interrupted, Problem-Based Learning



Subject Headings

Biochemistry  |   Biology (General)  |   Cell Biology  |   Ecology  |   Genetics / Heredity  |   Microbiology  |   Molecular Biology  |  

Date Posted


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