Crocins belong to the apocarotenoid glycosides and are the main bioactive components in saffron, derived from the stigmas of Crocus sativus. Under the need for efficient and economical methods for producing crocins, microbial production enhances the possibility of fabrication of crocins. Four major heterologous enzymes were introduced in S.cerevisiae for simulating the crocin biosynthetic pathway. β-carotene hydroxylase (CrtZ), carotenoid cleavage dioxygenase (CCD), aldehyde dehydrogenase (ALDH), and two types of UDP-glucosyltransferases (UGTs) were expressed, including novel enzymes that were isolated by our group. A qualitative-quantitative analysis of the precursor was performed at each step to find the optimal catalytic activities among candidate enzymes from different organism sources. As a result, the metabolic engineered S.cerevisiae strain produced 65.23 ± 2.97μg/L of crocin-4 in flask cultivation. To increase the supply of UDP-glucose, two genes named pgm2, ugp1 involved in endogenous uridine diphosphate glucose pathway were over-expressed respectively in S. cerevisiae. As a result, overexpression of a pgm2 gene encoding phosphoglucomutase enhanced 2.1 fold increase in crocin-4 from 65.23 ± 2.97μg/L to 136.17 ± 5.89μg/L in flask cultivation. Finally, a batch culture operated under the conditions (20℃, pH 5.5, and a DO of 40%) enhanced up to 204.25 ± 8.83 μg/L of crocin-4 in a bioreactor. To the best of our knowledge, our study presents the first crocin-producing S. cerevisiae cell factory.
