Trends in in-silico guided engineering of efficient polyethylene terephthalate (PET) hydrolyzing enzymes to enable bio-recycling and upcycling of PET.

Polyethylene terephthalate (PET) is the largest produced polyester globally, and less than 30% of all the PET produced globally (∼6 billion pounds annually) is currently recycled into lower-quality products. The major drawbacks in current recycling methods (mechanical and chemical), have inspired the exploration of potentially efficient and sustainable PET depolymerization using biological approaches. Researchers have discovered efficient PET hydrolyzing enzymes in the plastisphere and have demonstrated the selective degradation of PET to original monomers thus enabling biological recycling or upcycling. However, several significant hurdles such as the less efficiency of the hydrolytic reaction, low thermostability of the enzymes, and the inability of the enzyme to depolymerize crystalline PET must be addressed in order to establish techno-economically feasible commercial-scale biological PET recycling or upcycling processes. Researchers leverage a synthetic biology-based design; build, test, and learn (DBTL) methodology to develop commercially applicable efficient PET hydrolyzing enzymes through 1) high-throughput metagenomic and proteomic approaches to discover new PET hydrolyzing enzymes with superior properties: and, 2) enzyme engineering approaches to modify and optimize PET hydrolyzing properties. Recently, in-silico platforms including molecular mechanics and machine learning concepts are emerging as innovative tools for the development of more efficient and effective PET recycling through the exploration of novel mutations in PET hydrolyzing enzymes. In-silico-guided PET hydrolyzing enzyme engineering with DBTL cycles enables the rapid development of efficient variants of enzymes over tedious conventional enzyme engineering methods such as random or directed evolution. This review highlights the potential of in-silico-guided PET degrading enzyme engineering to create more efficient variants, including Ideonella sakaiensis PETase (IsPETase) and leaf-branch compost cutinases (LCC). Furthermore, future research prospects are discussed to enable a sustainable circular economy through the bioconversion of PET to original or high-value platform chemicals.

Repurposing of waste PET by microbial biotransformation to functionalized materials for additive manufacturing.

Plastic waste is an outstanding environmental thread. Poly(ethylene terephthalate) (PET) is one of the most abundantly produced single-use plastics worldwide, but its recycling rates are low. In parallel, additive manufacturing is a rapidly evolving technology with wide-ranging applications. Thus, there is a need for a broad spectrum of polymers to meet the demands of this growing industry and address post-use waste materials. This perspective article highlights the potential of designing microbial cell factories to upcycle PET into functionalized chemical building blocks for additive manufacturing. We present the leveraging of PET hydrolyzing enzymes and rewiring the bacterial C2 and aromatic catabolic pathways to obtain high-value chemicals and polymers. Since PET mechanical recycling back to original materials is cost-prohibitive, the biochemical technology is a viable alternative to upcycle PET into novel 3D printing materials, such as replacements for acrylonitrile butadiene styrene. The presented hybrid chemo-bio approaches potentially enable the manufacturing of environmentally friendly degradable or higher-value high-performance polymers and composites and their reuse for a circular economy. ONE-SENTENCE SUMMARY: Biotransformation of waste PET to high-value platform chemicals for additive manufacturing.

Opportunities in the microbial valorization of sugar industrial organic waste to biodegradable smart food packaging materials.

Many petroleum-derived plastics, including food packaging materials are non-biodegradable and designed for single-use applications. Annually, around 175 Mt. of plastic enters the land and ocean ecosystems due to mismanagement and lack of techno economically feasible plastic waste recycling technologies. Renewable sourced, biodegradable polymer-based food packaging materials can reduce this environmental pollution. Sugar production from sugarcane or sugar beet generates organic waste streams that contain fermentable substrates, including sugars, acids, and aromatics. Microbial metabolism can be leveraged to funnel those molecules to platform chemicals or biopolymers to generate biodegradable food packaging materials that have active or sensing molecules embedded in biopolymer matrices. The smart package can real-time monitor food quality, assure health safety, and provide economic and environmental benefits. Active packaging materials display functional properties such as antimicrobial, antioxidant, and light or gas barrier. This article provides an overview of potential biodegradable smart/active polymer packages for food applications by valorizing sugar industry-generated organic waste. We highlight the potential microbial pathways and metabolic engineering strategies to biofunnel the waste carbon efficiently into the targeted platform chemicals such as lactic, succinate, muconate, and biopolymers, including polyhydroxyalkanoates, and bacterial cellulose. The obtained platform chemicals can be used to produce biodegradable polymers such as poly (butylene adipate-co-terephthalate) (PBAT) that could replace incumbent polyethylene and polypropylene food packaging materials. When nanomaterials are added, these polymers can be active/smart. The process can remarkably lower the greenhouse gas emission and energy used to produce food-packaging material via sugar industrial waste carbon relative to the petroleum-based production. The proposed green routes enable the valorization of sugar processing organic waste into biodegradable materials and enable the circular economy.

Valorization of sugar beet pulp to value-added products: A review.

The processing of sugar beet in the sugar production industry releases huge amounts of sugar beet pulp as waste which can be considered a valuable by-product as a source of cellulose, hemicellulose, and pectin. Valorization of sugar beet pulp into value added products occurs through acid hydrolysis, hydrothermal techniques, and enzymatic hydrolysis. Biochemical conversion of beet pulp into simple fermentable sugars for producing value added products occurs through enzymatic hydrolysis is a cost effective and eco-friendly process. While beet pulp has predominantly been used as a fodder for livestock, recent developments in its biotechnological valorization have unlocked its value as a feedstock in the production of biofuels, biohydrogen, biodegradable plastics, and platform chemicals such as lactic acid, citric acid, alcohols, microbial enzymes, single cell proteins, and pectic oligosaccharides. This review brings forward recent biotechnological developments made in the valorization of sugar beet pulp into valuable products.

Trends in valorization of highly-toxic lignocellulosic biomass derived-compounds via engineered microbes.

Lignocellulosic biomass-derived fuels, chemicals, and materials are promising sustainable solutions to replace the current petroleum-based production. The direct microbial conversion of thermos-chemically pretreated lignocellulosic biomass is hampered by the presence of highly toxic chemical compounds. Also, thermo-catalytic upgrading of lignocellulosic biomass generates wastewater that contains heterogeneous toxic chemicals, a mixture of unutilized carbon. Metabolic engineering efforts have primarily focused on the conversion of carbohydrates in lignocellulose biomass; substantial opportunities exist to harness value from toxic lignocellulose-derived toxic compounds. This article presents the comprehensive metabolic routes and tolerance mechanisms to develop robust synthetic microbial cell factories to valorize the highly toxic compounds to advanced-platform chemicals. The obtained platform chemicals can be used to manufacture high-value biopolymers and biomaterials via a hybrid biochemical approach for replacing petroleum-based incumbents. The proposed strategy enables a sustainable bio-based materials economy by microbial biofunneling of lignocellulosic biomass-derived toxic molecules, an untapped biogenic carbon.

Biological upgrading of pyrolysis-derived wastewater: Engineering Pseudomonas putida for alkylphenol, furfural, and acetone catabolism and (methyl)muconic acid production.

While biomass-derived carbohydrates have been predominant substrates for biological production of renewable fuels, chemicals, and materials, organic waste streams are growing in prominence as potential alternative feedstocks to improve the sustainability of manufacturing processes. Catalytic fast pyrolysis (CFP) is a promising approach to generate biofuels from lignocellulosic biomass, but it generates a complex, carbon-rich, and toxic wastewater stream that is challenging to process catalytically but could be biologically upgraded to valuable co-products. In this work, we implemented modular, heterologous catabolic pathways in the Pseudomonas putida KT2440-derived EM42 strain along with the overexpression of native toxicity tolerance machinery to enable utilization of 89% (w/w) of carbon in CFP wastewater. The dmp monooxygenase and meta-cleavage pathway from Pseudomonas putida CF600 were constitutively expressed to enable utilization of phenol, cresols, 2- and 3-ethyl phenol, and methyl catechols, and the native chaperones clpB, groES, and groEL were overexpressed to improve toxicity tolerance to diverse aromatic substrates. Next, heterologous furfural and acetone utilization pathways were incorporated, and a native alcohol dehydrogenase was overexpressed to improve methanol utilization, generating reducing equivalents. All pathways (encoded by genes totaling ~30 kilobases of DNA) were combined into a single strain that can catabolize a mock CFP wastewater stream as a sole carbon source. Further engineering enabled conversion of all aromatic compounds in the mock wastewater stream to (methyl)muconates with a ~90% (mol/mol) yield. Biological upgrading of CFP wastewater as outlined in this work provides a roadmap for future applications in valorizing other heterogeneous waste streams.

Engineering Microbes to Bio-Upcycle Polyethylene Terephthalate.

Polyethylene terephthalate (PET) is globally the largest produced aromatic polyester with an annual production exceeding 50 million metric tons. PET can be mechanically and chemically recycled; however, the extra costs in chemical recycling are not justified when converting PET back to the original polymer, which leads to less than 30% of PET produced annually to be recycled. Hence, waste PET massively contributes to plastic pollution and damaging the terrestrial and aquatic ecosystems. The global energy and environmental concerns with PET highlight a clear need for technologies in PET "upcycling," the creation of higher-value products from reclaimed PET. Several microbes that degrade PET and corresponding PET hydrolase enzymes have been successfully identified. The characterization and engineering of these enzymes to selectively depolymerize PET into original monomers such as terephthalic acid and ethylene glycol have been successful. Synthetic microbiology and metabolic engineering approaches enable the development of efficient microbial cell factories to convert PET-derived monomers into value-added products. In this mini-review, we present the recent progress of engineering microbes to produce higher-value chemical building blocks from waste PET using a wholly biological and a hybrid chemocatalytic-biological strategy. We also highlight the potent metabolic pathways to bio-upcycle PET into high-value biotransformed molecules. The new synthetic microbes will help establish the circular materials economy, alleviate the adverse energy and environmental impacts of PET, and provide market incentives for PET reclamation.

In-depth understanding of molecular mechanisms of aldehyde toxicity to engineer robust Saccharomyces cerevisiae.

Aldehydes are ubiquitous electrophilic compounds that ferment microorganisms including Saccharomyces cerevisiae encounter during the fermentation processes to produce food, fuels, chemicals, and pharmaceuticals. Aldehydes pose severe toxicity to the growth and metabolism of the S. cerevisiae through a variety of toxic molecular mechanisms, predominantly via damaging macromolecules and hampering the production of targeted compounds. Compounds with aldehyde functional groups are far more toxic to S. cerevisiae than all other functional classes, and toxic potency depends on physicochemical characteristics of aldehydes. The yeast synthetic biology community established a design-build-test-learn framework to develop S. cerevisiae cell factories to valorize the sustainable and renewable biomass, including the lignin-derived substrates. However, thermochemically pretreated biomass-derived substrate streams contain diverse aldehydes (e.g., glycolaldehyde and furfural), and biological conversions routes of lignocellulosic compounds consist of toxic aldehyde intermediates (e.g., formaldehyde and methylglyoxal), and some of the high-value targeted products have aldehyde functional group (e.g., vanillin and benzaldehyde). Numerous studies comprehensively characterized both single and additive effects of aldehyde toxicity via systems biology investigations, and novel molecular approaches have been discovered to overcome the aldehyde toxicity. Based on those novel approaches, researchers successfully developed synthetic yeast cell factories to convert lignocellulosic substrates to valuable products, including aldehyde compounds. In this mini-review, we highlight the salient relationship of physicochemical characteristics and molecular toxicity of aldehydes, the molecular detoxification and macromolecules protection mechanisms of aldehydes, and the advances of engineering robust S. cerevisiae against complex mixtures of aldehyde inhibitors. KEY POINTS: • We reviewed structure-activity relationships of aldehyde toxicity on S. cerevisiae. • Two-tier protection mechanisms to alleviate aldehyde toxicity are presented. • We highlighted the strategies to overcome the synergistic toxicity of aldehydes.

Deletion of JEN1 and ADY2 reduces lactic acid yield from an engineered Saccharomyces cerevisiae, in xylose medium, expressing a heterologous lactate dehydrogenase.

Microorganisms have evolved to produce specific end products for many reasons, including maintaining redox balance between NAD+ and NADH. The yeast Saccharomyces cerevisiae, for example, produces ethanol as a primary end product from glucose for the regeneration of NAD+. Engineered S. cerevisiae strains have been developed to ferment lignocellulosic sugars, such as xylose, to produce lactic acid by expression of a heterologous lactate dehydrogenase (ldhA from Rhizopus oryzae) without genetic perturbation to the native ethanol pathway. Surprisingly, the engineered yeast strains predominantly produce ethanol from glucose, but produce lactic acid as the major product from xylose. Here, we provide initial evidence that the shift in product formation from ethanol to lactic acid during xylose fermentation is at least partially dependent on the presence of functioning monocarboxylate transporter genes/proteins, including JEN1 and ADY2, which are downregulated and unstable in the presence of glucose, but upregulated/stable on xylose. Future yeast metabolic engineering studies may find the feedstock/carbon selection, such as xylose, an important step toward improving the yield of target end products.

Laboratory evolution reveals the metabolic and regulatory basis of ethylene glycol metabolism by Pseudomonas putida KT2440.

Pollution from ethylene glycol, and plastics containing this monomer, represent a significant environmental problem. The investigation of its microbial metabolism therefore provides insights into the environmental fate of this pollutant and also enables its utilization as a carbon source for microbial biotechnology. Here, we reveal the genomic and metabolic basis of ethylene glycol metabolism in Pseudomonas putida KT2440. Although this strain cannot grow on ethylene glycol as sole carbon source, it can be used to generate growth-enhancing reducing equivalents upon co-feeding with acetate. Mutants that utilize ethylene glycol as sole carbon source were isolated through adaptive laboratory evolution. Genomic analysis of these mutants revealed a central role of the transcriptional regulator GclR, which represses the glyoxylate carboligase pathway as part of a larger metabolic context of purine and allantoin metabolism. Secondary mutations in a transcriptional regulator encoded by PP_2046 and a porin encoded by PP_2662 further improved growth on ethylene glycol in evolved strains, likely by balancing fluxes through the initial oxidations of ethylene glycol to glyoxylate. With this knowledge, we reverse engineered an ethylene glycol utilizing strain and thus revealed the metabolic and regulatory basis that are essential for efficient ethylene glycol metabolism in P. putida KT2440.

Expression of Gre2p improves tolerance of engineered xylose-fermenting Saccharomyces cerevisiae to glycolaldehyde under xylose metabolism.

Engineered S. cerevisiae employing the xylose reductase pathway enables efficient xylose valorization to fuels and chemicals. However, toxicity of thermochemically pretreated biomass hydrolysate on S. cerevisiae is one of the key technical challenges to upgrade biomass-derived sugars including xylose and glucose into high-value products. We investigated the effect of glycolaldehyde, one of the biomass-derived highly toxic aldehyde compounds, and its combinatorial inhibitory effect with other major fermentation inhibitors commonly found in plant hydrolysate such as methylglyoxal, 5-HMF, furfural, vanillin, and acetic acid on engineered xylose-fermenting S. cerevisiae in xylose and/or glucose media. We elucidated that glycolaldehyde and methylglyoxal are the key inhibitory short-aliphatic aldehydes on engineered xylose-fermenting S. cerevisiae in xylose-containing medium. Indeed, the degree of toxicity of these tested fermentation inhibitors varies with the sole carbon source of the medium. We demonstrate that genome integration of an extra copy of autologous GRE2 with its native promotor substantially improved the toxic tolerance of engineered xylose-fermenting S. cerevisiae to major inhibitory compounds including glycolaldehyde in the xylose-containing medium, and xylose-rich, lignocellulosic hydrolysate derived from Miscanthus giganteus, and concurrently improved the ethanol fermentation profile. Outcomes of this study will aid the development of next-generation robust S. cerevisiae strains for efficient fermentation of hexose and pentose sugars found in biomass hydrolysate.

Direct conversion of cellulose into ethanol and ethyl-ß-d-glucoside via engineered Saccharomyces cerevisiae.

Simultaneous saccharification and fermentation (SSF) of cellulose via engineered Saccharomyces cerevisiae is a sustainable solution to valorize cellulose into fuels and chemicals. In this study, we demonstrate the feasibility of direct conversion of cellulose into ethanol and a biodegradable surfactant, ethyl-ß-d-glucoside, via an engineered yeast strain (i.e., strain EJ2) expressing heterologous cellodextrin transporter (CDT-1) and intracellular ß-glucosidase (GH1-1) originating from Neurospora crassa. We identified the formation of ethyl-ß-d-glucoside in SSF of cellulose by the EJ2 strain owing to transglycosylation activity of GH1-1. The EJ2 strain coproduced 0.34 ± 0.03 g ethanol/g cellulose and 0.06 ± 0.00 g ethyl-ß-d-glucoside/g cellulose at a rate of 0.30 ± 0.02 g·L-1 ·h-1 and 0.09 ± 01 g·L-1 ·h-1 , respectively, during the SSF of Avicel PH-101 cellulose, supplemented only with Celluclast 1.5 L. Herein, we report a possible coproduction of a value-added chemical (alkyl-glucosides) during SSF of cellulose exploiting the transglycosylation activity of GH1-1 in engineered S. cerevisiae. This coproduction could have a substantial effect on the overall technoeconomic feasibility of theSSF of cellulose.

Engineering Pseudomonas putida KT2440 for efficient ethylene glycol utilization.

Ethylene glycol is used as a raw material in the production of polyethylene terephthalate, in antifreeze, as a gas hydrate inhibitor in pipelines, and for many other industrial applications. It is metabolized by aerobic microbial processes via the highly toxic intermediates glycolaldehyde and glycolate through C2 metabolic pathways. Pseudomonas putida KT2440, which has been engineered for environmental remediation applications given its high toxicity tolerance and broad substrate specificity, is not able to efficiently metabolize ethylene glycol, despite harboring putative genes for this purpose. To further expand the metabolic portfolio of P. putida, we elucidated the metabolic pathway to enable ethylene glycol via systematic overexpression of glyoxylate carboligase (gcl) in combination with other genes. Quantitative reverse transcription polymerase chain reaction demonstrated that all of the four genes in genomic proximity to gcl (hyi, glxR, ttuD, and pykF) are transcribed as an operon. Where the expression of only two genes (gcl and glxR) resulted in growth in ethylene glycol, improved growth and ethylene glycol utilization were observed when the entire gcl operon was expressed. Both glycolaldehyde and glyoxal inhibit growth in concentrations of ethylene glycol above 50 mM. To overcome this bottleneck, the additional overexpression of the glycolate oxidase (glcDEF) operon removes the glycolate bottleneck and minimizes the production of these toxic intermediates, permitting growth in up to 2 M (~124 g/L) and complete consumption of 0.5 M (31 g/L) ethylene glycol in shake flask experiments. In addition, the engineered strain enables conversion of ethylene glycol to medium-chain-length polyhydroxyalkanoates (mcl-PHAs). Overall, this study provides a robust P. putida KT2440 strain for ethylene glycol consumption, which will serve as a foundational strain for further biocatalyst development for applications in the remediation of waste polyester plastics and biomass-derived wastewater streams.

Identification and detoxification of glycolaldehyde, an unattended bioethanol fermentation inhibitor.

Although there have been approximately 60 chemical compounds identified as potent fermentation inhibitors in lignocellulose hydrolysate, our research group recently discovered glycolaldehyde as a key fermentation inhibitor during second generation biofuel production. Accordingly, we have developed a yeast S. cerevisiae strain exhibiting tolerance to glycolaldehyde. During this glycolaldehyde study, we established novel approaches for rational engineering of inhibitor-tolerant S. cerevisiae strains, including engineering redox cofactors and engineering the SUMOylation pathway. These new technical dimensions provide a novel platform for engineering S. cerevisiae strains to overcome one of the key barriers for industrialization of lignocellulosic ethanol production. As such, this review discusses novel biochemical insight of glycolaldehyde in the context of the biofuel industry.

Metabolic Engineering of Probiotic Saccharomyces boulardii.

Saccharomyces boulardiiis a probiotic yeast that has been used for promoting gut health as well as preventing diarrheal diseases. This yeast not only exhibits beneficial phenotypes for gut health but also can stay longer in the gut than Saccharomyces cerevisiae Therefore, S. boulardiiis an attractive host for metabolic engineering to produce biomolecules of interest in the gut. However, the lack of auxotrophic strains with defined genetic backgrounds has hampered the use of this strain for metabolic engineering. Here, we report the development of well-defined auxotrophic mutants (leu2,ura3,his3, and trp1) through clustered regularly interspaced short palindromic repeat (CRISPR)-Cas9-based genome editing. The resulting auxotrophic mutants can be used as a host for introducing various genetic perturbations, such as overexpression or deletion of a target gene, using existing genetic tools forS. cerevisiae We demonstrated the overexpression of a heterologous gene (lacZ), the correct localization of a target protein (red fluorescent protein) into mitochondria by using a protein localization signal, and the introduction of a heterologous metabolic pathway (xylose-assimilating pathway) in the genome ofS. boulardii We further demonstrated that human lysozyme, which is beneficial for human gut health, could be secreted by S. boulardii Our results suggest that more sophisticated genetic perturbations to improveS. boulardii can be performed without using a drug resistance marker, which is a prerequisite for in vivo applications using engineeredS. boulardii.

Mitigating health risks associated with alcoholic beverages through metabolic engineering.

Epidemiological studies have established a positive relationship between the occurrence of cancer and consumption of alcoholic beverages. Metabolic engineering of brewing yeast to reduce potential carcinogenic compounds in alcoholic beverage is technically feasible as well as economically promising. This review presents the mechanisms of formation of potentially carcinogenic components in alcoholic beverages, such as formaldehyde, acetaldehyde, ethyl carbamate, acrylamide, and heavy metals, and introduces effective genetic perturbations to minimize the concentrations of these harmful components. As precise and effective genome editing tools for polyploid yeast are now available, we envision that yeast metabolic engineering might open up new research directions for improving brewing yeast in order to ensure product safety as well as to increase overall quality of alcoholic beverages.

SUMO expression shortens the lag phase of Saccharomyces cerevisiae yeast growth caused by complex interactive effects of major mixed fermentation inhibitors found in hot-compressed water-treated lignocellulosic hydrolysate.

The complex inhibitory effects of inhibitors present in lignocellulose hydrolysate suppress the ethanol fermentation of Saccharomyces cerevisiae. Although the interactive inhibitory effects play important roles in the actual hydrolysate, few studies have investigated glycolaldehyde, the key inhibitor of hot-compressed water-treated lignocellulose hydrolysate. Given this challenge, we investigated the interactive effects of mixed fermentation inhibitors, including glycolaldehyde. First, we confirmed that glycolaldehyde was the most potent inhibitor in the hydrolysate and exerted interactive inhibitory effects in combination with major inhibitors. Next, through genome-wide analysis and megavariate data modeling, we identified SUMOylation as a novel potential mechanism to overcome the combinational inhibitory effects of fermentation inhibitors. Indeed, overall SUMOylation was increased and Pgk1, which produces an ATP molecule in glycolysis by substrate-level phosphorylation, was SUMOylated and degraded in response to glycolaldehyde. Augmenting the SUMO-dependent ubiquitin system in the ADH1-expressing strain significantly shortened the lag phase of growth, released cells from G2/M arrest, and improved energy status and glucose uptake in the inhibitor-containing medium. In summary, our study was the first to establish SUMOylation as a novel platform for regulating the lag phase caused by complex fermentation inhibitors.

Identification of the sulphate ion as one of the key components of yeast spoilage of a sports drink through genome-wide expression analysis.

Because of the growing market for sports drinks, prevention of yeast contamination of these beverages is of significant concern. This research was performed to achieve insight into the physiology of yeast growing in sports drinks through a genome-wide approach to prevent microbial spoilage of sports drinks. The genome-wide gene expression profile of Saccharomyces cerevisiae growing in the representative sports drink was investigated. Genes that were relevant to sulphate ion starvation response were upregulated in the yeast cells growing in the drink. These results suggest that yeast cells are suffering from deficiency of extracellular sulphate ions during growth in the sports drink. Indeed, the concentration of sulphate ions was far lower in the sports drink than in a medium that allows the optimal growth of yeast. To prove the starvation of sulphate ions of yeast, several ions were added to the beverage and its effects were investigated. The addition of sulphate ions, but not chloride ions or sodium ions, to the beverage stimulated yeast growth in the beverage in a dose-dependent manner. Moreover, the addition of sulphate ions to the sports drink increased the biosynthesis of sulphur-containing amino acids in yeast cells and hydrogen sulphide in the beverage. These results indicate that sulphate ion concentration should be regulated to prevent microbial spoilage of sports drinks.

Engineering redox cofactor utilization for detoxification of glycolaldehyde, a key inhibitor of bioethanol production, in yeast Saccharomyces cerevisiae.

Hot-compressed water treatment of lignocellulose liberates numerous inhibitors that prevent ethanol fermentation of yeast Saccharomyces cerevisiae. Glycolaldehyde is one of the strongest fermentation inhibitors and we developed a tolerant strain by overexpressing ADH1 encoding an NADH-dependent reductase; however, its recovery was partial. In this study, to overcome this technical barrier, redox cofactor preference of glycolaldehyde detoxification was investigated. Glycolaldehyde-reducing activity of the ADH1-overexpressing strain was NADH-dependent but not NADPH-dependent. Moreover, genes encoding components of the pentose phosphate pathway, which generates intracellular NADPH, was upregulated in response to high concentrations of glycolaldehyde. Mutants defective in pentose phosphate pathways were sensitive to glycolaldehyde. Genome-wide survey identified GRE2 encoding a NADPH-dependent reductase as the gene that confers tolerance to glycolaldehyde. Overexpression of GRE2 in addition to ADH1 further improved the tolerance to glycolaldehyde. NADPH-dependent glycolaldehyde conversion to ethylene glycol and NADP+ content of the strain overexpressing both ADH1 and GRE2 were increased at 5 mM glycolaldehyde. Expression of GRE2 was increased in response to glycolaldehyde. Carbon metabolism of the strain was rerouted from glycerol to ethanol. Thus, it was concluded that the overexpression of GRE2 together with ADH1 restores glycolaldehyde tolerance by augmenting the NADPH-dependent reduction pathway in addition to NADH-dependent reduction pathway. The redox cofactor control for detoxification of glycolaldehyde proposed in this study could influence strategies for improving the tolerance of other fermentation inhibitors.