Construction of l-Isoleucine Overproducing Strains of Corynebacterium glutamicum |
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Authors: | H Sahm L Eggeling S Morbach B Eikmanns |
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Institution: | Institut für Biotechnologie, Forschungszentrum Jülich GmbH, D-52425 Jülich, Germany, DE Institut für Biochemie, Universit?t K?ln, Zülpicher Strasse 47, D-50674 K?ln, Germany, DE Angewandte Mikrobiologie, Universit?t Ulm, D-89069 Ulm, Germany, DE
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Abstract: | Corynebacterium glutamicum is used for the industrial production of the amino acids l-glutamate (1×106 tons/year) and l-lysine (300×103 tons/year). The classical approach to obtain amino acid overproducing strains of C. glutamicum was mutagenesis and then a selection of mutants. In the past 10 years the genetic engineering and amplification of genes
have become fascinating methods for studying metabolic pathways in greater detail and for constructing microbial strains with
desired genotypes. To obtain l-isoleucine overproducing strains of C. glutamicum we therefore studied the l-isoleucine biosynthesis by overexpression of the various corresponding genes. To enable a flux increase in recombinant strains
all genes specific for l-threonine and l-isoleucine biosynthesis were cloned from this bacterium. We demonstratet that amplification of the feedback inhibition insensitive
homoserine dehydrogenase and homoserine kinase in a high l-lysine overproducing strain enable the channeling of the carbon flow from the intermediate l-aspartate semialdehyde towards homoserine, resulting in an accumulation of l-threonine. To obtain effective l-isoleucine overproduction a deregulated threonine dehydratase was overexpressed in l-threonine producing strains of C. glutamicum. In this way the l-threonine was converted to l-isoleucine, which was secreted up to 30 g/l into the culture medium.
Received: 7 April 1998 / Accepted in revised form: 27 August 1998 |
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