title: Mutations in MurE, the essential UDP-N-acetylmuramoylalanyl-D-glutamate 2,6-diaminopimelate ligase of Corynebacterium glutamicum: effect on L-lysine formation and analysis of systemic consequences.
abstract: OBJECTIVE
  To explore systemic effects of mutations in the UDP-N-acetylmuramoylalanyl-D-glutamate 2,6-diaminopimelate ligase (MurE) of Corynebacterium glutamicum, that leads to extracellular L-lysine accumulation by this bacterium.
  
  
  RESULTS
  The analysis of a mutant cohort of C. glutamicum strains carrying all possible 20 amino acids at position 81 of MurE revealed unexpected effects on cellular properties. With increasing L-lysine accumulation the growth rate of the producing strain is reduced. A dynamic flux balance analysis including the flux over MurE fully supports this finding and suggests that further reductions at this flux control point would enhance L-lysine accumulation even further. The strain carrying the best MurE variant MurE-G81K produces 37 mM L-lysine with a yield of 0.17 g/g (L-lysine·HCl/glucose·H2O), bearing no other genetic modification. Interestingly, among the strains with high L-lysine titers, strain variants occur which, despite possessing the desired amino acid substitutions in MurE, have regained close to normal growth and correspondingly lower L-lysine accumulation. Genome analyses of such variants revealed the transposition of mobile genetic elements which apparently annulled the favorable consequences of the MurE mutations on L-lysine formation.
  
  
  CONCLUSIONS
  MurE is an attractive target to achieve high L-lysine accumulation, and product formation is inversely related to the specific growth rate. Moreover, single point mutations leading to elevated L-lysine titers may cause systemic effects on different levels comprising also major genome modifications. The latter caused by the activity of mobile genetic elements, most likely due to the stress conditions being characteristic for microbial metabolite producers.
authors: IBG-1: Biotechnology, Institute of Bio- and Geosciences, Forschungszentrum Jülich GmbH, 52425, Jülich, Germany.
authors: Jennifer
authors: J
authors: Hochheim
authors: IBG-1: Biotechnology, Institute of Bio- and Geosciences, Forschungszentrum Jülich GmbH, 52425, Jülich, Germany.
authors: Angela
authors: A
authors: Kranz
authors: IBG-1: Biotechnology, Institute of Bio- and Geosciences, Forschungszentrum Jülich GmbH, 52425, Jülich, Germany.
authors: Karin
authors: K
authors: Krumbach
authors: IBG-1: Biotechnology, Institute of Bio- and Geosciences, Forschungszentrum Jülich GmbH, 52425, Jülich, Germany.
authors: Sascha
authors: S
authors: Sokolowsky
authors: IBG-1: Biotechnology, Institute of Bio- and Geosciences, Forschungszentrum Jülich GmbH, 52425, Jülich, Germany. l.eggeling@fz-juelich.de.
authors: Lothar
authors: http://orcid.org/0000-0001-7060-2806
authors: L
authors: Eggeling
authors: IBG-1: Biotechnology, Institute of Bio- and Geosciences, Forschungszentrum Jülich GmbH, 52425, Jülich, Germany.
authors: Stephan
authors: S
authors: Noack
authors: , Adalbertsteinweg 166, 52066, Aachen, Germany.
authors: Marco
authors: M
authors: Bocola
authors: IBG-1: Biotechnology, Institute of Bio- and Geosciences, Forschungszentrum Jülich GmbH, 52425, Jülich, Germany.
authors: Michael
authors: M
authors: Bott
authors: IBG-1: Biotechnology, Institute of Bio- and Geosciences, Forschungszentrum Jülich GmbH, 52425, Jülich, Germany. j.marienhagen@fz-juelich.de.
authors: Jan
authors: J
authors: Marienhagen
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D048230:Corynebacterium glutamicum / Q000201:enzymology* / Q000378:metabolism*; D008239:Lysine / Q000378:metabolism*; D010453:Peptide Synthases / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D010453:Peptide Synthases; D008239:Lysine
keywords: Amino acid production; Cell wall synthesis; L-Lysine technology; Mobile elements; Strain stability