title: Engineering of high yield production of L-serine in Escherichia coli.
abstract: L-serine is a widely used amino acid that has been proposed as a potential building block biochemical. The high theoretical yield from glucose makes a fermentation based production attractive. In order to achieve this goal, serine degradation to pyruvate and glycine in E. coli MG1655 was prevented by deletion of three L-serine deaminases sdaA, sdaB, and tdcG, as well as serine hydroxyl methyl transferase (SHMT) encoded by glyA. Upon overexpression of the serine production pathway, consisting of a feedback resistant version of serA along with serB and serC, this quadruple deletion strain showed a very high serine production yield (0.45 g/g glucose) during small-scale batch fermentation in minimal medium. Serine, however, was found to be highly toxic even at low concentrations to this strain, which lead to slow growth and production during fed batch fermentation, resulting in a serine production of 8.3 g/L. The production strain was therefore evolved by random mutagenesis to achieve increased tolerance towards serine. Additionally, overexpression of eamA, a cysteine/homoserine transporter was demonstrated to increase serine tolerance from 1.6 g/L to 25 g/L. During fed batch fermentation, the resulting strain lead to the serine production titer of 11.7 g/L with yield of 0.43 g/g glucose, which is the highest yield reported so far for any organism.
authors.affiliation: Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, Hørsholm, 2970, Denmark.
authors.forename: Hemanshu
authors.initials: H
authors.lastname: Mundhada
authors.affiliation: Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, Hørsholm, 2970, Denmark.
authors.forename: Konstantin
authors.initials: K
authors.lastname: Schneider
authors.affiliation: Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, Hørsholm, 2970, Denmark.
authors.forename: Hanne Bjerre
authors.initials: HB
authors.lastname: Christensen
authors.affiliation: Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, Hørsholm, 2970, Denmark. atn@biosustain.dtu.dk.
authors.forename: Alex Toftgaard
authors.initials: AT
authors.lastname: Nielsen
mesh_terms: D001692:Biological Transport; D004361:Drug Tolerance; D004926:Escherichia coli / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism*; D017353:Gene Deletion; D015870:Gene Expression; D060847:Metabolic Engineering / Q000379:methods*; D053858:Metabolic Networks and Pathways / Q000235:genetics; D009154:Mutation; D012694:Serine / Q000378:metabolism* / Q000633:toxicity
chemical_list: D012694:Serine
keywords: E. coli; L-serine production; L-serine toxicity; amino acids; fermentation; metabolic engineering