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Appl. Environ. Microbiol., 04 1995, 1391-1398, Vol 61, No. 4
J Kidwell, HE Valentin and D Dennis
A novel poly-beta-hydroxybutyrate (PHB) production system in which the
expression and gene dosage of the Alcaligenes eutrophus pha biosynthetic
operon were effectively regulated by cultivation temperature was
constructed in Escherichia coli. The pha operon was fused to the negatively
regulated tac promoter and cloned into a vector in which the copy number is
temperature dependent. A two-phase process was employed to produce PHB
during fed-batch growth. In the growth phase, the culture was maintained at
a low temperature. Under this condition, the plasmid copy number was
depressed and the number of LacI proteins was sufficient to repress tacupha
transcription. The production phase was initiated by temperature upshift.
At the elevated temperature, the number of plasmids surpassed the number of
LacI repressors, which resulted in rapid induction of tacupha
transcription, synthesis of poly-beta-hydroxyalkanoate-specific proteins,
and polymer synthesis. During the production phase, the PHB production rate
was 1.07 g of PHB liter-1 h-1 under optimized conditions. This rate is
comparable to that of bacteria which naturally produce this polymer.
Copyright © 1995, American Society for Microbiology
Regulated expression of the Alcaligenes eutrophus pha biosynthesis genes in Escherichia coli
Department of Biology, James Madison University, Harrisonburg, Virginia 22807, USA.
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