Affiliation:
1. Institut für Biotechnologie, Forschungszentrum Jülich, D-52425 Jülich, Germany
2. BIOTIKA, 976 13 Slovenská Lupc̆a, Slovakia
Abstract
ABSTRACT
Mutants of
Corynebacterium glutamicum
were made and enzymatically characterized to clone
ilvD
and
ilvE
, which encode dihydroxy acid dehydratase and transaminase B, respectively. These genes of the branched-chain amino acid synthesis were overexpressed together with
ilvBN
(which encodes acetohydroxy acid synthase) and
ilvC
(which encodes isomeroreductase) in the wild type, which does not excrete
l
-valine, to result in an accumulation of this amino acid to a concentration of 42 mM. Since
l
-valine originates from two pyruvate molecules, this illustrates the comparatively easy accessibility of the central metabolite pyruvate. The same genes,
ilvBNCD
, overexpressed in an
ilvA
deletion mutant which is unable to synthesize
l
-isoleucine increased the concentration of this amino acid to 58 mM. A further dramatic increase was obtained when
panBC
was deleted, making the resulting mutant auxotrophic for
d
-pantothenate. When the resulting strain,
C. glutamicum
13032ΔilvAΔpanBC with
ilvBNCD
overexpressed, was grown under limiting conditions it accumulated 91 mM
l
-valine. This is attributed to a reduced coenzyme A availability and therefore reduced flux of pyruvate via pyruvate dehydrogenase enabling its increased drain-off via the
l
-valine biosynthesis pathway.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
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