Production of the sesquiterpene (+)-valencene by metabolically engineered Corynebacterium glutamicum.

The sesquiterpene (+)-valencene is an aroma compound of citrus fruits and is used to flavor foods and drinks. Biosynthesis of (+)-valencene starts from farnesyl pyrophosphate, an intermediate of carotenoid biosynthesis. Corynebacterium glutamicum, the workhorse of the million-ton scale amino acid industry, is naturally pigmented as it synthesizes the rare fifty carbon atoms (C50) containing carotenoid decaprenoxanthin. Since the carotenoid pathway of this Gram-positive bacterium has previously been engineered for efficient production of several C50 and C40 carotenoids, its potential to produce a sesquiterpene was assessed. Growth of C. glutamicum was negatively affected by (+)-valencene, but overlaying n-dodecane as organic phase for extraction of (+)-valencene was shown to be biocompatible. Heterologous expression of the (+)-valencene synthase gene from the sweet orange Citrus sinensis was not sufficient to enable (+)-valencene production, likely because provision of farnesyl pyrophosphate (FPP) by endogenous prenyltransferases was too low. However, upon deletion of two endogenous prenyltransferase genes and heterologous expression of either FPP synthase gene ispA from Escherichia coli or ERG20 from Saccharomyces cerevisiae (+)-valence production by C. sinensis valencene synthase was observed. Employing the valencene synthase from Nootka cypress improved (+)-valencene titers 10 fold to 2.41±0.26mgl(-1) (+)-valencene, which is equivalent to 0.25±0.03mgg(-1) cell dry weight (CDW). This is the first report on sesquiterpene overproduction by recombinant C. glutamicum.
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