High production of valencene in Saccharomyces cerevisiae through metabolic engineering.
BACKGROUND
The biological synthesis of high value compounds in industry through metabolically engineered microorganism factories has received increasing attention in recent years. Valencene is a high value ingredient in the flavor and fragrance industry, but the low concentration in nature and high cost of extraction limits its application. Saccharomyces cerevisiae, generally recognized as safe, is one of the most commonly used gene expression hosts. Construction of S. cerevisiae cell factory to achieve high production of valencene will be attractive.


RESULTS
Valencene was successfully biosynthesized after introducing valencene synthase into S. cerevisiae BJ5464. A significant increase in valencene yield was observed after down-regulation or knock-out of squalene synthesis and other inhibiting factors (such as erg9, rox1) in mevalonate (MVA) pathway using a recyclable CRISPR/Cas9 system constructed in this study through the introduction of Cre/loxP. To increase the supplement of the precursor farnesyl pyrophosphate (FPP), all the genes of FPP upstream in MVA pathway were overexpressed in yeast genome. Furthermore, valencene expression cassettes containing different promoters and terminators were compared, and PHXT7-VS-TTPI1 was found to have excellent performance in valencene production. Finally, after fed-batch fermentation in 3 L bioreactor, valencene production titer reached 539.3 mg/L with about 160-fold improvement compared to the initial titer, which is the highest reported valencene yield.


CONCLUSIONS
This study achieved high production of valencene in S. cerevisiae through metabolic engineering and optimization of expression cassette, providing good example of microbial overproduction of valuable chemical products. The construction of recyclable plasmid was useful for multiple gene editing as well.
['Chen|Hefeng|H|', 'Zhu|Chaoyi|C|', 'Zhu|Muzi|M|', 'Xiong|Jinghui|J|', 'Ma|Hao|H|', 'Zhuo|Min|M|', 'Li|Shuang|S|http://orcid.org/0000-0001-6595-6175']
D064113:CRISPR-Cas Systems D060847:Metabolic Engineering D030781:Organisms, Genetically Modified D010957:Plasmids D012441:Saccharomyces cerevisiae D012717:Sesquiterpenes
Valencene Saccharomyces cerevisiae Metabolic engineering Expression cassette Recyclable plasmid Synthetic biology