A Two-Enzyme Adaptive Unit within Bacterial Folate Metabolism

Cell Rep. 2019 Jun 11;27(11):3359-3370.e7. doi: 10.1016/j.celrep.2019.05.030.


Enzyme function and evolution are influenced by the larger context of a metabolic pathway. Deleterious mutations or perturbations in one enzyme can often be compensated by mutations to others. We used comparative genomics and experiments to examine evolutionary interactions with the essential metabolic enzyme dihydrofolate reductase (DHFR). Analyses of synteny and co-occurrence across bacterial species indicate that DHFR is coupled to thymidylate synthase (TYMS) but relatively independent from the rest of folate metabolism. Using quantitative growth rate measurements and forward evolution in Escherichia coli, we demonstrate that the two enzymes adapt as a relatively independent unit in response to antibiotic stress. Metabolomic profiling revealed that TYMS activity must not exceed DHFR activity to prevent the depletion of reduced folates and the accumulation of the intermediate dihydrofolate. Comparative genomics analyses identified >200 gene pairs with similar statistical signatures of modular co-evolution, suggesting that cellular pathways may be decomposable into small adaptive units.

Keywords: DHFR; TYMS; adaptive unit; co-evolution; comparative genomics; dihydrofolate reductase; experimental evolution; folate metabolism; forward evolution; synteny; thymidylate synthase; trimethoprim.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptation, Physiological*
  • Escherichia coli
  • Escherichia coli Proteins / genetics*
  • Escherichia coli Proteins / metabolism
  • Evolution, Molecular*
  • Folic Acid / genetics
  • Folic Acid / metabolism*
  • Stress, Physiological
  • Synteny
  • Tetrahydrofolate Dehydrogenase / genetics*
  • Tetrahydrofolate Dehydrogenase / metabolism
  • Thymidylate Synthase / genetics*
  • Thymidylate Synthase / metabolism


  • Escherichia coli Proteins
  • Folic Acid
  • Tetrahydrofolate Dehydrogenase
  • Thymidylate Synthase