Metabolic Engineering of Saccharomyces cerevisiae for Enhanced Carotenoid Production From Xylose-Glucose Mixtures.

Buli Su,Dandan Song,Honghui Zhu

doi:10.3389/fbioe.2020.00435

Abstract

Co-utilization of xylose and glucose from lignocellulosic biomass is an economically feasible bioprocess for chemical production. Many strategies have been implemented for efficiently assimilating xylose which is one of the predominant sugars of lignocellulosic biomass. However, there were few reports about engineering Saccharomyces cerevisiae for carotenoid production from xylose-glucose mixtures. Herein, we developed a platform for facilitating carotenoid production in S. cerevisiae by fermentation of xylose-glucose mixtures. Firstly, a xylose assimilation pathway with mutant xylose reductase (XYL1m), xylitol dehydrogenase (XYL2), and xylulokinase (XK) was constructed for utilizing xylose. Then, introduction of phosphoketolase (PK) pathway, deletion of Pho13 and engineering yeast hexose transporter Gal2 were conducted to improve carotenoid yields. The final strain SC105 produced a 1.6-fold higher production from mixed sugars than that from glucose in flask culture. In fed-batch fermentation with continuous feeding of mixed sugars, carotenoid production represented a 2.6-fold higher. To the best of our knowledge, this is the first report that S. cerevisiae was engineered to utilize xylose-glucose mixtures for carotenoid production with a considerable high yield. The present study exhibits a promising advantage of xylose-glucose mixtures assimilating strain as an industrial carotenoid producer from lignocellulosic biomass.

Highlights

Glucose from starch hydrolysates was widely used as raw material in industrial biotechnology (Buschke et al, 2013)
In order to produce xylose-based carotenoid, the xyloseassimilating pathway including XYL1/XYL2 was introduced into the lycopene-producing strain S. cerevisiae BL03-D-4 to use xylose as a carbon source, which was necessary for xylosebased production
Acetyl-CoA is an important precursor for carotenoid synthesis and its biosynthesis was primary catalyzed by pyruvate decarboxylase (PDC), acetaldehyde dehydrogenase (Ald) and acetyl-CoA synthetase (ACS) in S. cerevisiae cytoplasm

Summary

Introduction

Glucose from starch hydrolysates was widely used as raw material in industrial biotechnology (Buschke et al, 2013). It is important to utilize both glucose and xylose from lignocellulosic biomass during manufacturing process for the economically feasible production of valuable chemicals. Nonxylose-assimilating S. cerevisiae has been extensively studied for bioethanol production from xylose in lignocellulosic biomass due to its remarkable alcoholic fermentation (Kwak et al, 2019). In this study, strain SC103 was constructed for improving carotenoid yield through introduction of PK pathway which included xylulose-5-phosphate phosphoketolase (xPK) and phosphotransacetylase (PTA) (Kocharin et al, 2013; Meadows et al, 2016). In the fermentation of mixed sugars, xylose was ideally consumed for biosynthesis of target products, while glucose was used for growth and supply cofactor (Su et al, 2015). The yield of carotenoid from xylose-glucose was 17.1 mg g−1 DCW, which represented a 1.4-fold higher than that from glucose (12.2 mg g−1 DCW)

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