Cellobiose Consumption Uncouples Extracellular Glucose Sensing and Glucose Metabolism in
            <i>Saccharomyces cerevisiae</i>

Chomvong, Kulika; Benjamin, D. M.; Nomura, Daniel K.; Cate, J.H.D.

doi:10.1128/mbio.00855-17

Cited by 11 publications

(11 citation statements)

References 45 publications

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“…Further research is required to test these ideas experimentally. In cellobiose-utilizing S. cerevisiae, limited activity of Pfk1 (which catalyzes the phosphorylation of fructose-6-phosphate) was found to be a major bottleneck in cellobiose consumption [60]. Identification of rate-limiting step(s) in glycolytic pathway during cellobiose utilization would facilitate the engineering of M. thermophila to produce biochemicals.…”

Section: Discussionmentioning

confidence: 99%

Metabolic engineering of the cellulolytic thermophilic fungus Myceliophthora thermophila to produce ethanol from cellobiose

Zhang

et al. 2020

Biotechnol Biofuels

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Background: Cellulosic biomass is a promising resource for bioethanol production. However, various sugars in plant biomass hydrolysates including cellodextrins, cellobiose, glucose, xylose, and arabinose, are poorly fermented by microbes. The commonly used ethanol-producing microbe Saccharomyces cerevisiae can usually only utilize glucose, although metabolically engineered strains that utilize xylose have been developed. Direct fermentation of cellobiose could avoid glucose repression during biomass fermentation, but applications of an engineered cellobiose-utilizing S. cerevisiae are still limited because of its long lag phase. Bioethanol production from biomass-derived sugars by a cellulolytic filamentous fungus would have many advantages for the biorefinery industry. Results: We selected Myceliophthora thermophila, a cellulolytic thermophilic filamentous fungus for metabolic engineering to produce ethanol from glucose and cellobiose. Ethanol production was increased by 57% from glucose but not cellobiose after introduction of ScADH1 into the wild-type (WT) strain. Further overexpression of a glucose transporter GLT-1 or the cellodextrin transport system (CDT-1/CDT-2) from N. crassa increased ethanol production by 131% from glucose or by 200% from cellobiose, respectively. Transcriptomic analysis of the engineered cellobioseutilizing strain and WT when grown on cellobiose showed that genes involved in oxidation-reduction reactions and the stress response were downregulated, whereas those involved in protein biosynthesis were upregulated in this effective ethanol production strain. Turning down the expression of pyc gene results the final engineered strain with the ethanol production was further increased by 23%, reaching up to 11.3 g/L on cellobiose. Conclusions: This is the first attempt to engineer the cellulolytic fungus M. thermophila to produce bioethanol from biomass-derived sugars such as glucose and cellobiose. The ethanol production can be improved about 4 times up to 11 grams per liter on cellobiose after a couple of genetic engineering. These results show that M. thermophila is a promising platform for bioethanol production from cellulosic materials in the future.

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Section: Discussionmentioning

confidence: 99%

Metabolic engineering of the cellulolytic thermophilic fungus Myceliophthora thermophila to produce ethanol from cellobiose

Zhang

et al. 2020

Biotechnol Biofuels

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“…While conventional approaches are successful for production of chemicals, which involves optimizing a single pathway, substrate assimilation is far more complicated as hundreds of metabolic, regulatory, and signaling pathways need to coordinate for fast growth. Moreover, stress and carbon starvation-like response during metabolism of sugars for which yeast do not have nutrient sensing systems, [54–56,119,120] highlights the importance of nutrient sensing in S. cerevisiae and has to be addressed. Re-routing native nutrient sensing systems to detect these non-native sugars through “Regulon Engineering” relieves the stress and starvation responses [120] and results in high growth rates [83,120] probably through activation of growth-related genes.…”

Section: Discussionmentioning

confidence: 99%

“…Since xylose is not a natively metabolizable sugar, it is possible that the required substrate signaling pathways are not triggered leading to carbon, and amino acid starvation signals . This kind of starvation response is not xylose‐specific and is also observed in yeast strains engineered for growth in cellobiose . It can be theorized that since cellobiose, a disaccharide made of glucose monomers is not detected by extracellular glucose sensors, but is metabolized internally by the glucose pathway, it results in a carbon starvation‐like condition.…”

Section: Comparing Native and Non‐native Sugar Metabolismmentioning

confidence: 99%

“…[54–56] This kind of starvation response is not xylose-specific and is also observed in yeast strains engineered for growth in cellobiose. [119] It can be theorized that since cellobiose, a disaccharide made of glucose monomers is not detected by extracellular glucose sensors, but is metabolized internally by the glucose pathway, it results in a carbon starvation-like condition.…”

Section: Comparing Native and Non-native Sugar Metabolismmentioning

confidence: 99%

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Pentose Metabolism in Saccharomyces cerevisiae: The Need to Engineer Global Regulatory Systems

Gopinarayanan

Nair

2018

Biotechnology Journal

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Extending the host substrate range of industrially relevant microbes, such as Saccharomyces cerevisiae, has been a highly-active area of research since the conception of metabolic engineering. Yet, rational strategies that enable non-native substrate utilization in this yeast without the need for combinatorial and/or evolutionary techniques are underdeveloped. Herein, this review focuses on pentose metabolism in S. cerevisiae as a case study to highlight the challenges in this field. In the last three decades, work has focused on expressing exogenous pentose metabolizing enzymes as well as endogenous enzymes for effective pentose assimilation, growth, and biofuel production. The engineering strategies that are employed for pentose assimilation in this yeast are reviewed, and compared with metabolism and regulation of native sugar, galactose. In the case of galactose metabolism, multiple signals regulate and aid growth in the presence of the sugar. However, for pentoses that are non-native, it is unclear if similar growth and regulatory signals are activated. Such a comparative analysis aids in identifying missing links in xylose and arabinose utilization. While research on pentose metabolism have mostly concentrated on pathway level optimization, recent transcriptomics analyses highlight the need to consider more global regulatory, structural, and signaling components.

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“…Secondary metabolite production usually commences at the late stages of microbial growth such as the stationary or resting phase in response to starvation [ 34 , 35 ]. On the other hand, a recent study revealed that the plasma membrane ATPase of cellobiose-fermenting yeast is in a carbon starvation-like state, in which the plasma membrane ATPase activates plasma membrane transporters and is closely related to glucose sensing [ 36 ]. Therefore, the higher levels of the metabolic intermediates associated with the GABA shunt pathway and secondary metabolite production may be related to the stress responses owing to the carbon starvation-like state of strain EJ4 during cellobiose fermentation (Fig.…”

Section: Discussionmentioning

confidence: 99%

Promiscuous activities of heterologous enzymes lead to unintended metabolic rerouting in Saccharomyces cerevisiae engineered to assimilate various sugars from renewable biomass

Yun

Liu

et al. 2018

Biotechnol Biofuels

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BackgroundUnderstanding the global metabolic network, significantly perturbed upon promiscuous activities of foreign enzymes and different carbon sources, is crucial for systematic optimization of metabolic engineering of yeast Saccharomyces cerevisiae. Here, we studied the effects of promiscuous activities of overexpressed enzymes encoded by foreign genes on rerouting of metabolic fluxes of an engineered yeast capable of assimilating sugars from renewable biomass by profiling intracellular and extracellular metabolites.ResultsUnbiased metabolite profiling of the engineered S. cerevisiae strain EJ4 revealed promiscuous enzymatic activities of xylose reductase and xylitol dehydrogenase on galactose and galactitol, respectively, resulting in accumulation of galactitol and tagatose during galactose fermentation. Moreover, during glucose fermentation, a trisaccharide consisting of glucose accumulated outside of the cells probably owing to the promiscuous and transglycosylation activity of β-glucosidase expressed for hydrolyzing cellobiose. Meanwhile, higher accumulation of fatty acids and secondary metabolites was observed during xylose and cellobiose fermentations, respectively.ConclusionsThe heterologous enzymes functionally expressed in S. cerevisiae showed promiscuous activities that led to unintended metabolic rerouting in strain EJ4. Such metabolic rerouting could result in a low yield and productivity of a final product due to the formation of unexpected metabolites. Furthermore, the global metabolic network can be significantly regulated by carbon sources, thus yielding different patterns of metabolite production. This metabolomic study can provide useful information for yeast strain improvement and systematic optimization of yeast metabolism to manufacture bio-based products.Electronic supplementary materialThe online version of this article (10.1186/s13068-018-1135-7) contains supplementary material, which is available to authorized users.

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Cellobiose Consumption Uncouples Extracellular Glucose Sensing and Glucose Metabolism in Saccharomyces cerevisiae

Cited by 11 publications

References 45 publications

Metabolic engineering of the cellulolytic thermophilic fungus Myceliophthora thermophila to produce ethanol from cellobiose

Metabolic engineering of the cellulolytic thermophilic fungus Myceliophthora thermophila to produce ethanol from cellobiose

Pentose Metabolism in Saccharomyces cerevisiae: The Need to Engineer Global Regulatory Systems

Promiscuous activities of heterologous enzymes lead to unintended metabolic rerouting in Saccharomyces cerevisiae engineered to assimilate various sugars from renewable biomass

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