Stable integration sites in Saccharomyces cerevisiae: identification and application in the biosynthesis of valencene

Abstract:

Valencene, a high-value sesquiterpene with a citrus aroma, is widely employed in the food and cosmetic fields and the industrial synthesis of nootkatone. In this study, 16 genomic loci in the intergenic regions (IGRs) of Saccharomyces cerevisiae were identified. A Ypet expression cassette was successfully integrated into various genomic loci by CRISPR-Cas9, with an impressive integration success rate of 87.50% and exhibiting expression variations of up to 1.91-fold depending on the insertion site. The study demonstrates that the positional effect exhibits relative stability in gene expression, and is essentially unaffected by changes in promoters and reporter genes. Furthermore, a high-expression element combination, P_TDH3-T_PRC1, was selected. The iterative integration of the valencene synthase gene VSm from Callitropsis nootkatensis at the selected loci increased the valencene yield to 254.67 mg/L. Overexpression of key genes tHMG1-ERG20 with multiple copies increased the valencene yield by 93.49%. The engineered strain L-13 achieved the valencene yield of 9 530.18 mg/L by two-stage fed-batch fermentation in a 3 L fermenter. This yield represents a nearly 100-fold increase compared with that of the starting strain, highlighting the significant potential of the screened genomic loci in optimizing valencene production.