d‐Xylose consumption by nonrecombinant Saccharomyces cerevisiae: A review

Abstract

Xylose is the second most abundant sugar in nature. Its efficient fermentation has been considered as a critical factor for a feasible conversion of renewable biomass resources into biofuels and other chemicals. The yeast Saccharomyces cerevisiae is of exceptional industrial importance due to its excellent capability to ferment sugars. However, although S. cerevisiae is able to ferment xylulose, it is considered unable to metabolize xylose, and thus, a lot of research has been directed to engineer this yeast with heterologous genes to allow xylose consumption and fermentation. The analysis of the natural genetic diversity of this yeast has also revealed some nonrecombinant S. cerevisiae strains that consume or even grow (modestly) on xylose. The genome of this yeast has all the genes required for xylose transport and metabolism through the xylose reductase, xylitol dehydrogenase, and xylulokinase pathway, but there seems to be problems in their kinetic properties and/or required expression. Self‐cloning industrial S. cerevisiae strains overexpressing some of the endogenous genes have shown interesting results, and new strategies and approaches designed to improve these S. cerevisiae strains for ethanol production from xylose will also be presented in this review.

Combining Xylose Reductase from Spathaspora arborariae with Xylitol Dehydrogenase from Spathaspora passalidarum to Promote Xylose Consumption and Fermentation into Xylitol by Saccharomyces cerevisiae

“…Although the recombinant strain produced no acetate (and consequently the pH of the medium dropped just to pH 4.5) and less xylitol and ethanol, the production of glycerol was only slightly increased ( Figure 2, Table 6), indicating that other factors may limit xylose utilization by our engineered yeast strains. For example, the bottleneck may be a consequence of the relatively low affinity of the cloned SpXYL2.2 xylitol dehydrogenase for both NAD + and xylitol (Table 4), or the intracellular pools of reduced or oxidized and NADH/NADPH ratio of co-substrates [49,50], or even the low affinity of yeast sugar permeases for xylose transport [5,14,51]. Nevertheless, the ASY-2 strain transformed with the pPGK-SaXYL1 and pTEF-SpXYL2.2 plasmids (Table 6) showed xylitol yields (Y p/s = 0.614 g xylitol/g xylose) and volumetric productivities (Q p = 0.513 g/L/h) as good as or superior to those reported by other naturally xylose fermenting yeasts [52][53][54][55] or even engineered S. cerevisiae strains [38,49,50].…”

“…are the hexose d-glucose and the pentose d-xylose. To develop an economically feasible industrial process, it is necessary to efficiently consume and metabolize both sugars [3,4], in a scenario where xylose is not as readily consumed as glucose by the Saccharomyces yeasts [5]. The efficient consumption of pentose sugars is, therefore, important in the overall bioconversion of plant biomass for the production of liquid fuels and chemicals.…”

“…The discovery of xylose-fermenting yeasts in the early 1980s [7,8] was considered a milestone, with numerous xylose-fermenting yeasts been reported, and some even improved, over the following years [9]. While most bacteria and some fungi convert, directly, xylose into xylulose through a xylose isomerase, in the case of the yeasts known as being capable of xylose utilization, its metabolism occurs via a xylose reductase and xylitol dehydrogenase [10], followed by a xylulokinase that channels xylulose into the pentose-phosphate pathway [5]. While the xylose reductase/xylitol dehydrogenase pathway may present unbalanced co-substrate requirements for these two enzymes, and thus xylitol accumulation and secretion, it is more thermodynamically advantageous than the xylose isomerase pathway, allowing faster xylose assimilation by engineered yeast strains [11,12].…”

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

“…Thus, transport might be a bottleneck, especially in the xylose-glucose mixtures. In previous studies, engineering transports were used to improve engineered strains further (Patino et al, 2019). To facilitate xylose metabolism, the mutant hexose transporter Gal2 (N376F, not inhibited by glucose) (Farwick et al, 2014) was overexpressed with the promoter replacement with SSA1 in strain SC104 to obtain SC105.…”

Metabolic regulation adapting to high methanol environment in the methylotrophic yeast Ogataea methanolica

“…Among them, methylotrophic yeasts, such as Komagataella phaffii (formerly Pichia pastoris [Kurtzman, 2005]), Candida boidinii , Ogataea polymorpha (formerly Hansenula polymorpha [Yamada et al, 1994]), and Ogataea methanolica (formerly Pichia methanolica [Kurtzman and Robnett, 1998]), have high potential as fermentation producers for several biomass conversions from methanol. They are recognized as attractive hosts for the production of heterologous protein for the following reasons: (i) the yeast is easy to grow to a high‐density culture; (ii) abundant molecular genetic tools are available; (iii) the yeast has strong methanol‐inducible promoters for the gene expression system; (iv) the yeast has the advantages of performing extensive post‐translational modifications, protein folding and secretion of recombinant targets; and (v) the yeast possesses higher tolerance to extreme (acidic and basic) pH conditions (Porro et al ., 2005; Cos et al ., 2006; Yurimoto et al ., 2011; Palma et al ., 2018; Tan et al, 2018; Patiño et al ., 2019; Fabarius et al, 2021).…”