Hyperproduction of L-threonine by an escherichia coli mutant with impaired L-threonine uptake

Kazuyuki Okamoto, Kuniki Kino, Masato Ikeda

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Abstract

An efficient production strain for L-threonine fermentation was derived from Escherichia coli by multiple rounds of mutation programs that aimed at deregulation of the L-threonine biosynthetic pathway and blocking of L-threonine degradation pathways. When the optimum amount of DL-methionine was added, this strain KYI0935, an L-methionine auxotroph, gave 100g/liter L-threonine after 77 h cultivation. In this strain, key enzymes in the L-threonine biosynthetic pathway were highly derepressed, but some were inhibited by lower concentrations of L-threonine than the accumulated level. Such incomplete deregulation of the pathway was accounted for by the intracellular concentration of L-threonine being lower than the extracellular level. In an assessment of L-threonine transport in terms of phenotypic growth responses to the amino acid, L-threonine-auxotrophic mutants with a lesion in the L-threonine operon were derived from strain KY10935 by selection for auxotrophy for dipeptide L-alanyl-L-threonine or glycyl-L-threonine, the transport systems of which were different from those of L-threonine. All three independent mutants isolated needed an extraordinarily high concentration (10mg/ml) of L-threonine, but grew in the presence of a low concentration (10 μg/ml) of either dipeptide, indicating that strain KY10935 had impaired L-threonine uptake. These results suggested that the strain had an unusual mechanism of L-threonine hyperproduction: the inability to take up L-threonine that had accumulated extracellularly decreased the steady-state level of intracellular L-threonine, freeing the remaining regulatory steps of feedback inhibition.

Original languageEnglish
Pages (from-to)1877-1882
Number of pages6
JournalBioscience, Biotechnology and Biochemistry
Volume61
Issue number11
DOIs
Publication statusPublished - 1997 Jan

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Keywords

  • Strain improvement
  • Threonine production
  • Threonine uptake
  • Transport mutant of Escherichia coli

ASJC Scopus subject areas

  • Biotechnology
  • Analytical Chemistry
  • Biochemistry
  • Applied Microbiology and Biotechnology
  • Molecular Biology
  • Organic Chemistry

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