title: Why metabolic enzymes are essential or nonessential for growth of Escherichia coli K12 on glucose.
abstract: The genes encoding metabolic enzymes involved in glucose metabolism, the TCA cycle, and biosynthesis of amino acids, purines, pyrimidines, and cofactors would be expected to be essential for growth of Escherichia coli on glucose because the cells must synthesize all of the building blocks for cellular macromolecules. Surprisingly, 80 of 227 of these genes are not essential. Analysis of why these genes are not essential provides insights into the metabolic sophistication of E. coli and into the evolutionary pressures that have shaped its physiology. Alternative routes enabled by interconnecting pathways can allow a defective step to be bypassed. Isozymes, alternative enzymes, broad-specificity enzymes, and multifunctional enzymes can often substitute for a missing enzyme. We expect that the apparent redundancy in these metabolic pathways has arisen due to the need for E. coli to survive in a variety of habitats and therefore to have a metabolism that allows optimal exploitation of varying environmental resources and synthesis of small molecules when they cannot be obtained from the environment.
authors.affiliation: Cooperative Institute for Research in Environmental Sciences and Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, Colorado 80309, USA.
authors.forename: Juhan
authors.initials: J
authors.lastname: Kim
authors.forename: Shelley D
authors.initials: SD
authors.lastname: Copley
mesh_terms: D000596:Amino Acids / Q000378:metabolism; D002952:Citric Acid Cycle; D048168:Escherichia coli K12 / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development*; D015964:Gene Expression Regulation, Bacterial; D005943:Gluconeogenesis / Q000235:genetics*; D005947:Glucose / Q000378:metabolism*; D006019:Glycolysis / Q000235:genetics*; D007527:Isoenzymes / Q000235:genetics / Q000502:physiology; D053858:Metabolic Networks and Pathways; D008954:Models, Biological; D011687:Purines / Q000378:metabolism; D011743:Pyrimidines / Q000378:metabolism
chemical_list: D000596:Amino Acids; D007527:Isoenzymes; D011687:Purines; D011743:Pyrimidines; D005947:Glucose