Verlag des Forschungszentrums Jülich
JUEL-3606
Reuter, Uwe
Genetische und physiologische Untersuchungen zur Pantothenat- und Valinbildung in Corynebacterium glutamicum
115 S., 1998
Corynebacterium glutamicum wird seit vielen Jahren zur großtechnischen G
ewinnung der Aminosäuren L-Glutamat und L-Lysin eingesetzt. Ziel der vorliegenden
Arbeit war es, erstmals die Pantothenatbildung in C. glutamicum zu untersuchen
und die Valin- und Pantothenatgewinnung zu steigern, um somit die Voraussetzungen
für eine mikrobielle Produktion dieser beiden wirtschaftlich sehr interessanten
Substanzen zu schaffen.
The Gram-positive bacterium Corynebacterium glutamicum is used for the
production of amino acids, e.g. of L-glutamate and L-Iysine. The aim of my work
was to elucidate the biosynthetic pathway of pantothenic acid of this organism,
and to increase the formation of L-valine and D-pantothenic acid in order to
enable a microbiological production of these compounds.
The genes panB and panC were cloned, which encode the ketopantoatehydroxy-
methyltransferase and the pantothenatesynthetase. The two enzymes catalyze
important steps of the biosynthetic pathway of pantothenate. Sequence analysis
revealed that panB comprises 813 bp and panC 837 bp. The genes are organized
as an operon. Assays for the enzymes of the pathway have been developed. The
pantothenatesynthetase has a specific activity of 1 nmol/(min*mg protein), the
ketopantoatehydroxymethyltransferase one of 0.14 nmol/(min*mg protein) and the
aspartate-a-decarboxylase one of 0.11 nmol/(min*mg protein). The quantitative
analysis of the formation of pantothenic acid revealed that C. glutamicum
accumulates 10 µg/l pantothenic acid. A system to isolate mutants with an
increased formation of pantothenate, which is based on a deficiency of
pantothenic acid induced by [alpha]-ketobutyrate, has been established. The
application of this method led to the isolation of a mutant which accumulates 250
µg/l pantothenate and 1.4 g/l valine. Overexpression of the genes of the valine
and isoleucine biosynthetic pathway (ilvBNCD), in combination with the deletion of
the threonine dehydratase gene ilvA resulted in the construction of a strain which
accumulates 11,3 g/l valine and 190 mg/1 pantothenate. Additional overexpression
of panBC led to an accumulation of up to 1 g/l pantothenic acid. Thus an increase
of the formation of pantothenic acid in C. glutamicum by the factor of 105 has been
achieved.
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