[Dynamic control of ERG20 expression to improve production of monoterpenes by engineering Saccharomyces cerevisiae]

Monoterpenes are widely used in cosmetics, food, medicine, agriculture and other fields. With the development of synthetic biology, it is considered as a potential way to create microbial cell factories to produce monoterpenes. Engineering Saccharomyces cerevisiae to produce monoterpenes has been a research hotspot in synthetic biology. In S. cerevisiae, the production of geranyl pyrophosphate(GPP) and farnesyl pyrophosphate(FPP) is catalyzed by a bifunctional enzyme farnesyl pyrophosphate synthetase(encoded by ERG20 gene) which is inclined to synthesize FPP essential for yeast growth. Therefore, reasonable control of FPP synthesis is the basis for efficient monoterpene synthesis in yeast cell factories. In order to achieve dynamic control from GPP to FPP biosynthesis in S. cerevisiae, we obtained a novel chassis strain HP001-pERG1-ERG20 by replacing the ERG20 promoter of the chassis strain HP001 with the promoter of cyclosqualene cyclase(ERG1) gene. Further, we reconstructed the metabolic pathway by using GPP and neryl diphosphate(NPP), cis-GPP as substrates in HP001-pERG1-ERG20. The yield of GPP-derived linalool increased by 42.5% to 7.6 mg·L~(-1), and that of NPP-derived nerol increased by 1 436.4% to 8.3 mg·L~(-1). This study provides a basis for the production of monoterpenes by microbial fermentation.

Dynamic Control of ERG20 and ERG9 Expression for Improved Casbene Production in Saccharomyces cerevisiae

Production of plant metabolites in microbial hosts represents a promising alternative to traditional chemical-based methods. Diterpenoids are compounds with interesting applications as pharmaceuticals, fragrances and biomaterials. Casbene, in particular, serves as a precursor to many complex diterpenoids found in plants from the Euphorbiaceae family that have shown potential therapeutic effects. Here, we engineered the budding yeast Saccharomyces cerevisiae for improved biosynthesis of the diterpene casbene. We first expressed, in yeast, a geranylgeranyl diphosphate synthase from Phomopsys amygdali in order to boost the geranylgeranyl diphosphate pool inside the cells. The enzyme uses isopentenyl diphosphate and dimethylallyl diphosphate to directly generate geranylgeranyl diphosphate. When co-expressing a casbene synthase from Ricinus communis the yeast was able to produce casbene in the order of 30 mg/L. Redirecting the flux from FPP and sterols, by means of the ergosterol sensitive promoter of ERG1, allowed for plasmid-based casbene production of 81.4 mg/L. Integration of the target genes into the yeast genome, together with the replacement of the promoter regions of ERG20 and ERG9 with combinations of ergosterol- and glucose-sensitive promoters, generated a titer of 108.5 mg/L of casbene. We here succeeded to engineer an improved route for geranylgeranyl diphosphate synthesis in yeast. Furthermore, we showed that the concurrent dynamic control of ERG20 and ERG9 expression, using ergosterol and carbon source regulation mechanisms, could substantially improve diterpene titer. Our approach will pave the way for a more sustainable production of GGPP- and casbene-derived products.

Engineering Saccharomyces cerevisiae for the production of the valuable monoterpene ester geranyl acetate

Background

Geranyl acetate is widely used in the fragrance and cosmetic industries, and thus has great economic value. However, plants naturally produce a mixture of hundreds of esters, and geranyl acetate is usually only present in trace amounts, which makes its economical extraction from plant sources practically impossible. As an ideal host for heterologous production of fragrance compound, the Saccharomyces cerevisiae has never been engineered to produce the esters, such as geranyl acetate.

Results

In this study, a heterologous geranyl acetate synthesis pathway was constructed in S. cerevisiae for the first time, and a titer of 0.63 mg/L geranyl acetate was achieved. By expressing an Erg20 mutant to divert carbon flux from FPP to GPP, the geranyl acetate production increased to 2.64 mg/L. However, the expression of heterologous GPP had limited effect. The highest production of 13.27 mg/L geranyl acetate was achieved by additional integration and expression of tHMG1, IDI1 and MAF1. Furthermore, through optimizing fermentation conditions, the geranyl acetate titer increased to 22.49 mg/L.

Conclusions

We constructed a monoterpene ester producing cell factory in S. cerevisiae for the first time, and demonstrated the great potential of this system for the heterologous production of a large group of economically important fragrance compounds.

Electronic supplementary material

The online version of this article (10.1186/s12934-018-0930-y) contains supplementary material, which is available to authorized users.

Dynamic control of ERG20 expression combined with minimized endogenous downstream metabolism contributes to the improvement of geraniol production in Saccharomyces cerevisiae

BACKGROUND

Microbial production of monoterpenes provides a promising substitute for traditional chemical-based methods, but their production is lagging compared with sesquiterpenes. Geraniol, a valuable monoterpene alcohol, is widely used in cosmetic, perfume, pharmaceutical and it is also a potential gasoline alternative. Previously, we constructed a geraniol production strain by engineering the mevalonate pathway together with the expression of a high-activity geraniol synthase.

RESULTS

In this study, we further improved the geraniol production through reducing the endogenous metabolism of geraniol and controlling the precursor geranyl diphosphate flux distribution. The deletion of OYE2 (encoding an NADPH oxidoreductase) or ATF1 (encoding an alcohol acetyltransferase) both involving endogenous conversion of geraniol to other terpenoids, improved geraniol production by 1.7-fold or 1.6-fold in batch fermentation, respectively. In addition, we found that direct down-regulation of ERG20 expression, the branch point regulating geranyl diphosphate flux, does not improve geraniol production. Therefore, we explored dynamic control of ERG20 expression to redistribute the precursor geranyl diphosphate flux and achieved a 3.4-fold increase in geraniol production after optimizing carbon source feeding. Furthermore, the combination of dynamic control of ERG20 expression and OYE2 deletion in LEU2 prototrophic strain increased geraniol production up to 1.69 g/L with pure ethanol feeding in fed-batch fermentation, which is the highest reported production in engineered yeast.

CONCLUSION

An efficient geraniol production platform was established by reducing the endogenous metabolism of geraniol and by controlling the flux distribution of the precursor geranyl diphosphate. The present work also provides a production basis to synthesis geraniol-derived chemicals, such as monoterpene indole alkaloids.