title: Fine-tuning citrate synthase flux potentiates and refines metabolic innovation in the Lenski evolution experiment.
abstract: Evolutionary innovations that enable organisms to colonize new ecological niches are rare compared to gradual evolutionary changes in existing traits. We discovered that key mutations in the gltA gene, which encodes citrate synthase (CS), occurred both before and after Escherichia coli gained the ability to grow aerobically on citrate (Cit(+) phenotype) during the Lenski long-term evolution experiment. The first gltA mutation, which increases CS activity by disrupting NADH-inhibition of this enzyme, is beneficial for growth on the acetate and contributed to preserving the rudimentary Cit(+) trait from extinction when it first evolved. However, after Cit(+) was refined by further mutations, this potentiating gltA mutation became deleterious to fitness. A second wave of beneficial gltA mutations then evolved that reduced CS activity to below the ancestral level. Thus, dynamic reorganization of central metabolism made colonizing this new nutrient niche contingent on both co-opting and overcoming a history of prior adaptation.
authors.affiliation: Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, United States.|BEACON Center for the Study of Evolution in Action, Michigan State University, East Lansing, United States.
authors.forename: Erik M
authors.identifier: http://orcid.org/0000-0002-3287-7777
authors.initials: EM
authors.lastname: Quandt
authors.affiliation: Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, United States.
authors.forename: Jimmy
authors.initials: J
authors.lastname: Gollihar
authors.affiliation: BEACON Center for the Study of Evolution in Action, Michigan State University, East Lansing, United States.|Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, United States.
authors.forename: Zachary D
authors.initials: ZD
authors.lastname: Blount
authors.affiliation: Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, United States.|BEACON Center for the Study of Evolution in Action, Michigan State University, East Lansing, United States.|Department of Molecular Biosciences, The University of Texas at Austin, Austin, United States.|Center for Systems and Synthetic Biology, The University of Texas at Austin, Austin, United States.
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Ellington
authors.affiliation: Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, United States.|Department of Molecular Biosciences, The University of Texas at Austin, Austin, United States.|Department of Chemical Engineering, The University of Texas at Austin, Austin, United States.|Department of Biomedical Engineering, The University of Texas at Austin, Austin, United States.
authors.forename: George
authors.initials: G
authors.lastname: Georgiou
authors.affiliation: Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, United States.|BEACON Center for the Study of Evolution in Action, Michigan State University, East Lansing, United States.|Department of Molecular Biosciences, The University of Texas at Austin, Austin, United States.|Center for Systems and Synthetic Biology, The University of Texas at Austin, Austin, United States.|Center for Computational Biology and Bioinformatics, The University of Texas at Austin, Austin, United States.
authors.forename: Jeffrey E
authors.identifier: http://orcid.org/0000-0003-0888-7358
authors.initials: JE
authors.lastname: Barrick
mesh_terms: D000220:Adaptation, Biological; D000332:Aerobiosis; D002950:Citrate (si)-Synthase / Q000235:genetics* / Q000378:metabolism*; D019343:Citric Acid / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism*; D009154:Mutation
chemical_list: D019343:Citric Acid; D002950:Citrate (si)-Synthase
keywords: E. coli; epistasis; evolutionary biology; evolutionary innovation; experimental evolution; flux balance analysis; genetic basis of adaptation; genomics; metabolic network