Abstract
Xylose is the second most abundant sugar in lignocellulosic hydrolysates. Transformation of xylose into valuable chemicals, such as plant natural products, is a feasible and sustainable route to industrializing biorefinery of biomass materials. Yeast strains, including Saccharomyces cerevisiae, Scheffersomyces stipitis, and Yarrowia lipolytica, display some paramount advantages in expressing heterologous enzymes and pathways from various sources and have been engineered extensively to produce natural products. In this review, we summarize the advances in the development of metabolically engineered yeasts to produce natural products from xylose, including aromatics, terpenoids, and flavonoids. The state-of-the-art metabolic engineering strategies and representative examples are reviewed. Future challenges and perspectives are also discussed on yeast engineering for commercial production of natural products using xylose as feedstocks.
Highlights
Biomass hydrolysates are frequently used as a feedstock in biomass-based biorefinery
The xylose reductase (XR)-xylitol dehydrogenase (XDH) route is the mostly explored in recombinant yeasts owing to its ease of expression and high metabolic flux, and this route has been successfully expressed in non-xylose-fermenting yeasts including Sa. cerevisiae and Y. lipolytica (Kim et al, 2013; Wu et al, 2019)
To some special characteristics of certain yeast strains, such as moderate tolerance to toxic inhibitors in lignocellulosic hydrolysates, and moderate compatibility of heterologous pathway genes derived from both prokaryotes and eukaryotes
Summary
Biomass hydrolysates are frequently used as a feedstock in biomass-based biorefinery The conversion of these hydrolysates to useful compounds, such as natural products, is usually carried out by yeasts due to their advantageous properties such as tolerance of toxic inhibitors in hydrolysates, functional expression of eukaryote-derived heterologous pathways, and resistance to osmotic stress and harmful fermentation stimuli (Kwak et al, 2019; Li et al, 2019). Xylose cannot be naturally metabolized by the commonly used yeast chassis such as Saccharomyces cerevisiae and Yarrowia lipolytica with the exception of Scheffersomyces stipitis (Jagtap and Rao, 2018). To overcome this difficulty, there have been many attempts over the past few decades on yeast engineering for xylose fermentation, with Sa. cerevisiae as the main focus (Hou et al, 2017). Researchers started to explore yeast-based conversion of xylose, together with glucose, into value-added chemicals that are not readily available through extraction or chemical synthesis (Kwak and Jin, 2017; Kwak et al, 2019)
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