Abstract
β-carotene is a natural pigment and health-promoting metabolite, and has
been widely used in the nutraceutical, feed and cosmetic industries.
Here, we engineered a GRAS yeast Saccharomyces cerevisiae to
produce β-carotene from xylose, the second most abundant and inedible
sugar component of lignocellulose biomass. Specifically, a β-carotene
biosynthetic pathway containing crtYB, crtI and
crtE from Xanthophyllomyces dendrorhous were introduced
into a xylose-fermenting S. cerevisiae. The resulting strain
produced β-carotene from xylose at a titer three-fold higher than from
glucose. Interestingly, overexpression of tHMG1, which has been reported
as a critical genetic perturbation to enhance metabolic fluxes in the
mevalonate (MVA) pathway and β-carotene production in yeast when glucose
is used, did not further improve the production of β-carotene from
xylose. Through fermentation profiling, metabolites analysis and
transcriptional studies, we found the advantages of using xylose as a
carbon source instead of glucose for β-carotene production to be a more
respiratory feature of xylose consumption, a larger cytosolic acetyl-CoA
pool, and up-regulated expression levels of rate-limiting genes in the
β-carotene producing pathway, including ACS1 and HMG1. As a result,
772.81 mg/L of β-carotene was obtained in a fed-batch bioreactor culture
with xylose feeding. Considering the inevitable production of xylose at
large scales when cellulosic biomass-based bioeconomy is implemented,
our results suggest xylose utilization is a promising strategy for
overproduction of carotenoids and other isoprenoids in engineered
S. cerevisiae.