Biotechnology for Biofuels

The transition to sustainable bioeconomy requires efficient methods to identify microbial strains capable of deconstructing plant biomass. CAZyXplorer is an R Shiny platform designed to facilitate preliminary assessment of bacterial and fungal strains for industrial biorefinery applications based on carbohydrate-active enzyme (CAZy) annotation profiles. The platform uses multi-criteria decision analysis to evaluate over 200 enzyme families across six degradation pathways: cellulolytic, hemi-cellulolytic, ligninolytic, pectinolytic, starch-degrading, and inulin-degrading. CAZyXplorer implements weighted scoring algorithms that prioritize industrially relevant enzyme combinations, allocating 80% combined weighting to cellulolytic and hemi-cellulolytic activities. The tool calculates Shannon diversity indices to assess enzymatic repertoire completeness and includes interactive network analysis to visualize enzyme family distributions that may indicate degradation potential across different feedstocks. It is important to note that CAZyme gene counts reflect genomic potential rather than actual enzyme activity or expression levels. CAZyXplorer offers an accessible tool for researchers to perform comparative analysis of CAZyme profiles across multiple genomes. The platform has potential applications in initial screening for biofuel production, biochemical manufacturing, and other circular economy initiatives. CAZyXplorer serves as a preliminary analysis tool to guide strain selection decisions, complementing rather than replacing empirical screening and biochemical characterization in microbial bioprospecting for sustainable industrial biotechnology. The source code for the CAZyXplorer package is available at https://github.com/aysistak89/CAZyXplorer.

Lytic polysaccharide monooxygenases (LPMOs) are crucial industrial enzymes required in the biorefinery industry as well as in natural carbon cycle. These enzymes known to possess auxiliary activity are produced by numerous bacterial and fungal species to assist in the degradation of cellulosic biomass. In this study, we annotated and performed structural analysis of an uncharacterized thermostable LPMO from Penicillium funiculosum (PfLPMO9) in an attempt to understand nature of this enzyme in biomass degradation. PfLPMO9 exhibited 75% and 36% structural identity to Thermoascus aurantiacus (TaLPMO9A) and Lentinus similis (LsLPMO9A), respectively. Analysis of the molecular interactions during substrate binding revealed that PfLPMO9 demonstrated a higher binding affinity with a {Delta}G free energy of -46 k kcal/mol when compared with that of TaLPMO9A (-31 kcal/mol). The enzyme was further found to be highly thermostable at elevated temperature with a half-life of [~]88 h at 50 {degrees}C. Furthermore, multiple fungal genetic manipulation tools were employed to simultaneously overexpress this LPMO and Cellobiohydrolase I (CBH1) in catabolite derepressed strain of Penicillium funiculosum, PfMig188, in order to improve its saccharification performance towards acid pretreated wheat straw (PWS) at 20% substrate loading. The resulting transformants showed [~]200% and [~]66% increase in LPMO and Avicelase activities, respectively. While the secretomes of individually overexpressed LPMO and CBH1-strains increased saccharification of PWS by 6% and 13%, respectively, over PfMig188 at same enzyme concentration, the simultaneous overexpression of these two genes led to 20% increase in saccharification efficiency over PfMig188, which accounted for 82% saccharification of PWS at 20% substrate loading. ImportanceEnzymatic hydrolysis of cellulosic biomass by cellulases continues to be a significant bottleneck in the development of second-generation bio-based industries. While efforts are being intensified at how best to obtain indigenous cellulase for biomass hydrolysis, the high production cost of this enzyme remains a crucial challenge confronting its wide availability for efficient utilization of cellulosic materials. This is because it is challenging to get an enzymatic cocktail with balanced activity from a single host. This report provides for the first time the annotation and structural analysis of an uncharacterized thermostable lytic polysaccharide monooxygenase (LPMO) gene in Penicillium funiculosum and its impact in biomass deconstruction upon overexpression in catabolite derepressed strain of P. funiculosum. Cellobiohydrolase I (CBH1) which is the most important enzyme produced by many cellulolytic fungi for saccharification of crystalline cellulose was further overexpressed simultaneously with the LPMO. The resulting secretome was analyzed for enhanced LPMO and exocellulase activities with the corresponding improvement in its saccharification performance at high substrate loading by [~]20% using a minimal amount of protein.

Consolidated bioprocessing (CBP) of lignocellulosic biomass using cellulolytic microorganisms presents a promising sustainable and economical biomanufacturing platform where enzyme production, biomass hydrolysis, and fermentation to produce biofuels, biochemicals, and biomaterials occur in a single step. However, understanding and redirecting metabolism of microorganisms to be compatible with CBP to produce non-native metabolites are limited. In this study, we metabolically engineered a cellulolytic thermophile Clostridium thermocellum and demonstrated its compatibility with CBP integrated with a mild Co-solvent Enhanced Lignocellulosic Fractionation (CELF) pretreatment for conversion of hardwood poplar into short-chain esters (i.e., ethyl acetate, ethyl isobutyrate, isobutyl acetate, isobutyl isobutyrate) with broad use as solvents, flavors, fragrances, and biofuels. A recombinant C. thermocellum engineered with deletion of carbohydrate esterases and stable overexpression of a thermostable alcohol acetyltransferase improved the target esters production without compromised deacetylation activities. We discovered these esterases exhibited promiscuous thioesterase activities and their deletion improved ester production by increasing isobutanol flux and rerouting the native electron and carbon fermentative metabolism besides their known major function of ester degradation. The total ester production could be further enhanced up to 80-fold and the composition of short-chain esters could be modified by deleting lactate biosynthesis and/or CELF-pretreated poplar under different pretreatment conditions.

Integrated metabolic engineering approaches combining system and synthetic biology tools allow the efficient designing of microbial cell factories to synthesize high-value products. In the present study, in silico design algorithms were used on the latest yeast genome-scale model 8.5.0 to predict potential genomic modifications that could enhance the production of early-step Taxol(R) in previously engineered Saccharomyces cerevisiae cells. The solution set containing genomic modification candidates was narrowed down by employing the COnstraints Based Reconstruction and Analysis (COBRA) methods. 17 genomic modifications consisting of nine gene deletions and eight gene overexpression were screened using wet-lab studies to determine whether these modifications can increase the production yield of taxadiene, the first metabolite in the Taxol(R) through the mevalonate pathway. Depending on the cultivation condition, most of the single genomic modifications resulted in higher taxadiene production. The best-performing strain, named KM32, contained four overexpressed genes, ILV2, TRR1, ADE13 and ECM31, from the branched-chain amino acid biosynthesis, thioredoxin system, de novo purine synthesis, and the pantothenate pathway, respectively. Using KM32, taxadiene production was increased by 50%, reaching 215 mg/L of taxadiene. The engineered strain also produced 43.65 mg/L of taxa-4(20),11-dien-5-ol (T5-ol), and 26.2 mg/L of taxa-4(20),11-dien-5--yl acetate (T5Ac) which are the highest productions of these early-step Taxol(R) metabolites reported until now in S. cerevisiae. The findings of this study highlight that the use of computational and integrated approaches can ensure determining promising modifications that are difficult to estimate intuitively to develop yeast cell factories.

The oleaginous yeast Rhodotorula toruloides is a promising host for sustainable bioproduction due to its capacity to naturally utilize xylose present in lignocellulosic biomass, an abundant and renewable resource. However, its xylose consumption pathway is still not completely understood. To better understand the potential limitations in xylose utilization in R. toruloides, heterologous xylose reductase from Scheffersomyces stipitis, together with the native and heterologous xylulokinases from three different microorganisms (Scheffersomyces stipitis, Candida intermedia, and Escherichia coli) were overexpressed solely and in combination. The overexpression of xylulokinases showed more significant improvements in terms of xylose consumption rate compared to the single overexpression of xylose reductase. When the heterologous xylulokinase from Escherichia coli was overexpressed, the specific xylose consumption rate was improved by 66% and the maximum specific growth rate by 30% compared to the parental strain. The xylose specific consumption rate increased by 146% and the maximum specific growth rate increased by 118% when heterologous genes for xylose reductase and xylulokinase from E. coli were overexpressed together. These results suggest that the low expression of xylulokinase in R. toruloides, which has been reported previously, could limit its sugar consumption, while supporting higher lipid accumulation in this yeast.

Saccharomyces cerevisiae is an excellent microbial platform for sustainable production of next generation biofuels such as the branched chain higher alcohols (BCHAs) isobutanol and isopentanol. A cytosolic pathway for BCHA production is generated from expression of prokaryotic orthologs of branched-chain amino acid (BCAA) enzymes acetolactate synthase (ALS), mutant NADH-dependent ketol-acid reductoisomerase (KARIP2D1-A1), and dihydroxy-acid dehydratase (DHAD). The potential for this pathway has been hindered by the availability of iron-sulfur clusters, particularly the 2Fe-2S cluster, required for DHAD to function in the cytosol. ILV3, the endogenous yeast DHAD located in the mitochondria, can be deleted to create a valine auxotroph. In this study we use bioinformatics, heterologous gene library synthesis, and a valine complementation assay to find prokaryotic iron-sulfur cluster biosynthetic gene clusters (BGC) and accessory genes that aid DHAD function in the yeast cytosol. This work presents, to our knowledge, the first functional BGC that enhances the cytosolic activity of prokaryotic DHADs in S. cerevisiae. The SUF BGC from Bacillus subtilis combined with a ferritin-like protein (FTNB) from Escherichia coli and the Lactococcus lactis DHAD enhanced the production of BCHAs. Combined expression gave an average isobutanol titer of 412mg/L, 1.8-fold greater than L. lactis DHAD expressed alone. This work establishes a blueprint for better biofuel production by improving iron-sulfur cluster dependent enzyme activity in the yeast cytosol.

Lignocellulosic biomass represents a promising renewable feedstock for sustainable biorefinery applications, yet efficient enzymatic saccharification remains challenging due to the recalcitrant structure of plant cell walls. This study presents a comprehensive comparative analysis of enzymatic activities, saccharification performance, and secretome composition of six fungal species cultivated under solid-state fermentation (SSF) and submerged fermentation (SmF) conditions using untreated flax shives as substrate. While SmF yielded approximately 4-fold higher total protein concentrations (0.38 {+/-} 0.13 g.L-1 vs. 0.08 {+/-} 0.02 g.L-1), SSF-derived enzymes demonstrated superior specific enzymatic activities, particularly for endo-xylanase and endo-cellulase, resulting in more efficient biomass saccharification. Proteomics analysis revealed distinct secretome profiles between fermentation modes, with SSF showing higher proportions of polysaccharide metabolism proteins (71.0%) compared to SmF (49.3%), while SmF exhibited greater enzyme diversity including more lytic polysaccharide monooxygenases (LPMOs) and auxiliary activity enzymes. Trichoderma species consistently demonstrated the highest saccharification efficiency, with glucose yields reaching 2.37 mM under SSF conditions. A Scheffe simplex-lattice mixture design comprising 65 enzyme cocktail combinations revealed significant synergistic interactions between several cocktails, with the binary mixture of Trichoderma 2SA21 and P. chrysogenum achieving 54% synergy - in terms of higher sugar release above expectations - and the highest total monosaccharide release (1.80 mM). These findings provide practical guidance for developing cost-effective enzyme cocktails for lignocellulosic biorefinery applications, emphasizing the importance of fermentation mode selection and strategic strain combination over enzyme supplementation complexity. The methodology established here, combining systematic screening, comparative proteomics, and statistical mixture design, offers a robust framework for optimizing fungal enzyme systems across diverse biomass substrates. BULLET POINTSSuperior enzymatic activity (xylanase, cellulase) and saccharification in solid-state fermentation Superior total protein content and diversity in submerged fermentation Specific enzyme cocktails combination can lead to synergistic effects, justifying a combinatorial approach GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=107 SRC="FIGDIR/small/729743v1_ufig1.gif" ALT="Figure 1"> View larger version (25K): org.highwire.dtl.DTLVardef@1f3704dorg.highwire.dtl.DTLVardef@151e4bforg.highwire.dtl.DTLVardef@180ced7org.highwire.dtl.DTLVardef@18bb42f_HPS_FORMAT_FIGEXP M_FIG C_FIG

Ethanol production from renewable cellulosic materials is a globally significant research area. However, the high temperatures and acetic acid generated during cellulose pretreatment can inhibit Saccharomyces cerevisiae growth, reducing ethanol yields. This study investigates the impact of glutaredoxin family genes (GRXs) over-expression on S. cerevisiae cell growth and fermentation performance under thermal and acetic acid stress. Engineered strains overexpressing GRX1, GRX2, and GRX5 demonstrated enhanced growth at 42{degrees}C, while those overexpressing GRX1, GRX2, GRX6, and GRX7 showed improved growth at 1 g/L acetic acid. These results suggest that GRX over-expression can remediate S. cerevisiae, potentially accelerating advancements in green biomanufacturing.

Cannabis sativa has long been a cornerstone of both medicinal and cultural practices, with its therapeutic use spanning over 2,700 years. Central to its therapeutic effects are cannabinoids, which interact with the endocannabinoid system to influence various physiological processes such as anxiety, pain, and inflammation. Despite its benefits, cannabinoid production faces challenges and scarcity from plant extraction. This work leverages Yarrowia lipolytica as a platform for cannabinoid biosynthesis. By optimizing precursor supply, engineering biomolecular condensate-like dual prenyltransferase expression and expanding endogenous metabolism with a noncanonical polyketide synthase, we achieved the de novo biosynthesis of various cannabinoid and its analogs. Our engineered Y. lipolytica produced [~]3.5 mg/L of cannabigerolic acid, 18.8 mg/L of orsellinic acid, and 0.5 mg/L of cannabigerorcinic acid. Additionally, CBGA titer reached 15.7 mg/L with olivetolic acid supplement. This work demonstrates Y. lipolyticas versatility as a promising host for cannabinoid and its analogs production, which opens avenues for further research and medicinal applications.

Converting industrial side streams into value-added chemicals using microbial cell factories is of increasing interest, as such processes offer solutions to reduce waste and production costs. However, developing new, efficient cell factories for precision fermentation remains challenging due to limited knowledge about their metabolic capabilities. Here, we investigate the lactose and galactose metabolism of the non-conventional yeast Sungouiella intermedia (formerly Candida intermedia), using knowledge-matching of high-quality genome-scale metabolic model (GEM) with extensive experimental analysis and determine its potential as a future cell factory on lactose-rich industrial side-streams. We show that this yeast possesses the conserved Leloir pathway as well as an oxidoreductive galactose catabolic route. Contextualization of RNAseq data into Sint-GEM highlights the regulatory mechanisms on the oxidoreductive pathway and how this pathway can enable adaptation to diverse environments. Model simulations, together with experimental data from continuous and batch bioreactors, indicate that S. intermedia uses upstream enzymes of the oxidoreductive pathway, in a condition-dependent manner, and produce the sugar alcohol galactitol as a carbon overflow metabolite, coupled to redox co-factor balancing during both lactose and galactose growth. Furthermore, the new metabolic insights facilitated the development of an improved bioprocess design, where an engineered S. intermedia strain could achieve galactitol yields of >90% of the theoretical maximum at improved production rates using the industrial side-stream cheese whey permeate as feedstock. Additional strain engineering resulted in galactitol-to-tagatose conversion, proving the versatility of the future production host. Overall, this work sheds new light on the intrinsic interplay between parallel metabolic pathways that shape the lactose and galactose catabolism in S. intermedia. It also demonstrates how a GEM combined with experimental analysis can work in synergy to fast-forward metabolic characterization and development of new, non-conventional yeast cell factories. HighlightsO_LIAn oxidoreductive pathway functions in concert with the Leloir pathway for galactose catabolism. C_LIO_LIGEM predicts that galactitol secretion enables efficient carbon overflow metabolism and maintains redox balance. C_LIO_LIKnowledge-matching of GEM with experimental results highlights cell factory potential. C_LIO_LIHigh galactitol yields and proof-of-concept tagatose production using whey permeate as feedstock. C_LI

Cellulases are a group of enzymes with several applications in biofuel production, and the paper, food, pharmaceutical, and chemical industries. Trichoderma harzianum P49P11 secrete all cellulases with high efficiency, representing an alternative to the current filamentous fungi in biotechnological industries. In this study, the cellulolytic mechanisms employed by the strain P49P11 to degrade crystalline cellulose in batch fermentation culture mode were elucidated by combining genome and secretome analysis. The strain P49P11 encodes nineteen cellulase genes from five different CAZyme families (GH5, GH6, GH7, GH12, and GH45), followed by several enzyme families for hemicellulose, pectin, and alpha-and beta-glucans degradation. The diverse CAZymes were also observed in the secretome, including cellulases, hemicellulases, and glucanases. In addition, {beta}-glucosidases and xylanase activities detected during the fermentation process validated our secretome analysis. Taken together, our results revealed all enzymatic machinery used by the T. harzianum P49P11 to degrade cellulose in batch fermentation mode. HighlightsO_LIWe described a high-quality genome assembly and annotation of the T. harzianum P49P11. C_LIO_LIThe T. harzianum P49P11 genome possesses a complete set of genes for lignocellulose degradation. C_LIO_LIThe first report on T. harzianum P49P11 secretome obtained from batch fermentation strategy. C_LIO_LIT. harzianum P49P11 produced cellulases, lignocellulases, and auxiliary enzymes produced in response to crystalline cellulose. C_LI

Lavandulol and its ester derivative, lavandulyl acetate, are key fragrance constituents of lavender essential oil with widespread applications in cosmetics, perfumery, and food. However, traditional plant extraction suffers from low yield and unsustainable practices, and chemical synthesis relies on petrochemical feedstocks. Here, we report the first de novo microbial biosynthesis of lavandulol and lavandulyl acetate in Escherichia coli through modular pathway engineering. By screening 13 pyrophosphatases from E. coli, we identified RdgB as an efficient pyrophosphatase catalyzing the conversion of lavandulyl diphosphate into lavandulol, enabling its production at 24.9 mg/L. Building on this, we established a three-plasmid expression system and introduced a lavender-derived alcohol acyltransferase, LiAAT4, to achieve the biosynthesis of lavandulyl acetate at 42.4 mg/L. This study establishes the biosynthetic route to lavandulol in E. coli, demonstrating a viable and sustainable microbial platform for producing significant natural components of lavender oil. Our work provides the basis for future strain optimization and industrial-scale biomanufacturing of high-value monoterpene fragrance molecules.

The development of efficient, cost-effective bioreactor systems is pivotal in biotechnological processes involving the production of microbial products like pharmaceuticals, bio-fuels, and protein-rich biomass. Many bioreactor models are commercially available in all industries; however, prices are usually exorbitant, making them inaccessible to low-budget research, schools, and start-up companies. This article introduces a low-cost, DIY modular LSF bioreactor system intended to cultivate filamentous fungi and other microorganisms following a minimalist bubble column approach. Using standard sanitary tri-clamp (TC) fittings common in hygienic industries and household brewing setups, this assembly offers an affordable, adaptable, reparable, and robust solution for microbial production at a fraction of the cost of commercial alternatives. In addition, a wide range of budget-friendly sensors and controllers can be integrated to monitor and automate key parameters, making these bioreactors equally accessible and functional. This bubble column bioreactor concept is unique in its scalability and customization possibilities, significantly reducing research and prototyping costs.

BackgroundAmidst the escalating carbon dioxide levels resulting from fossil fuel consumption, there is a pressing need for sustainable, bio-based alternatives to underpin future global economies. Single carbon feedstocks, derived from CO2, represent promising substrates for biotechnological applications. Especially methanol is gaining prominence for bio-production of commodity chemicals. ResultsIn this study, we show the potential of Komagataella phaffii as a production platform for itaconic acid using methanol as the carbon source. Successful integration of heterologous genes from Aspergillus terreus (cadA, mttA and mfsA) alongside fine-tuning of the mfsA gene expression, led to promising initial itaconic acid titers of 28 g{middle dot}L-1 after five days of fed-batch cultivation. Through the combined efforts of process optimization and strain engineering strategies we further boosted the itaconic acid production reaching titers of 55 g{middle dot}L-1 after less than five days of methanol feed, whilst increasing the product yield on methanol from 0.06 g{middle dot}g- 1 to 0.24 g{middle dot}g-1. ConclusionOur results highlight the potential of K. phaffii as a methanol-based platform organism for sustainable biochemical production.

AO_SCPLOWBSTRACTC_SCPLOWSimultaneous intracellular depolymerization of xylo-oligosaccharides (XOS) and acetate fermentation by engineered Saccharomyces cerevisiae offers an advance towards more cost-effective second-generation (2G) ethanol production. As xylan is one of the most abundant polysaccharides present in lignocellulosic residues, the transport and breakdown of XOS in an intracellular environment might bring a competitive advantage for recombinant strains in competition with contaminating microbes, which are always present in fermentation tanks; furthermore, acetic acid is a ubiquitous toxic component in lignocellulosic hydrolysates, deriving from hemicellulose and lignin breakdown. In the present work, the previously engineered S. cerevisiae strain, SR8A6S3, expressing NADPH-linked xylose reductase (XR), NAD+-linked xylitol dehydrogenase (XDH) (for xylose assimilation), as well as NADH-linked acetylating acetaldehyde dehydrogenase (AADH) and acetyl-CoA synthetase (ACS) (for an NADH-dependent acetate reduction pathway), was used as the host for expressing of two {beta}-xylosidases, GH43-2 and GH43-7, and a xylodextrin transporter, CDT-2, from Neurospora crassa, yielding the engineered strain SR8A6S3-CDT2-GH432/7. Both {beta}-xylosidases and the transporter were introduced by replacing two endogenous genes, GRE3 and SOR1, that encode aldose reductase and sorbitol (xylitol) dehydrogenase, respectively, which catalyse steps in xylitol production. Xylitol accumulation during xylose fermentation is a problem for 2G ethanol production since it reduces final ethanol yield. The engineered strain, SR8A6S3-CDT2-GH432/7, produced ethanol through simultaneous co-utilization of XOS, xylose, and acetate. The mutant strain produced 60% more ethanol and 12% less xylitol than the control strain when a hemicellulosic hydrolysate was used as a mono- and oligosaccharide source. Similarly, the ethanol yield was 84% higher for the engineered strain using hydrolysed xylan compared with the parental strain. The consumption of XOS, xylose, and acetate expands the capabilities of S. cerevisiae for utilization of all of the carbohydrate in lignocellulose, potentially increasing the efficiency of 2G biofuel production. HighlightsO_LIIntegration of XOS pathway in an acetate-xylose-consuming S. cerevisiae strain; C_LIO_LIIntracellular fermentation of XOS, acetate and xylose improved ethanol production; C_LIO_LIDeletion of both sor1{Delta} and gre3{Delta} reduced xylitol production. C_LI

Corynebacterium glutamicum is a promising microbial chassis for the industrial production of L-tryptophan, which has exhibited increasing demand due to its diverse applications and high market value. In previous work, we developed an L-tryptophan-overproducing C. glutamicum strain TR26 through multiple rounds of rational metabolic engineering. Here, comparative transcriptome and metabolome analyses were conducted between TR26 and its progenitor strain MB001 to reveal the underlying mechanisms and potential bottlenecks for L-tryptophan production in TR26. Furthermore, by systematically down- and up-regulating differentially expressed genes of interest, two novel genetic targets, glnK and sugR, were identified as being associated with L-tryptophan synthesis. Specifically, the repression of glnK and overexpression of sugR in strain TR26 increased the titer of L-tryptophan by 6.7% and 20.9%, respectively. Gene transcription profiling and intracellular metabolite analysis further suggested that the observed improvements in L-tryptophan synthesis could be attributed to optimized nitrogen transport and metabolism, efficient reallocation of cellular resources and enhanced supply of phosphoenolpyruvate (PEP). This study advances our understanding of the regulation mechanisms governing L-tryptophan synthesis in C. glutamicum and provides valuable insights for further optimization of industrial cell factories.

Glycerol is an eco-friendly solvent enhancing plant-biomass decomposition through a glycerolysis process in many pretreatment methods. Nonetheless, the lack of efficient conversion of glycerol by natural Saccharomyces cerevisiae restrains many of these scenarios. Here we outline the complete strategy for the generation of efficient glycerol fermenting yeast by rewriting the oxidation of cytosolic nicotinamide adenine dinucleotide (NADH) by O2-dependent dynamic shuttle while abolishing both glycerol phosphorylation and biosynthesis pathways. By following a vigorous glycerol oxidative pathway, the engineered strain demonstrated augmentation in conversion efficiency (CE) reach up to 0.49g-ethanol/g-glycerol--98% of theoretical conversion--with production rate >1 g/L-1h-1 when supplementing glycerol as a single fed-batch on a rich-medium. Furthermore, the engineered strain showed a new capability toward ferment a mixture of glycerol and glucose with producing >86 g/L of bioethanol with 92.8% of the CE. To our knowledge, this is the highest ever reported titer in this regard. Notably, this strategy flipped our ancestral yeast from non-growth on glycerol, on the minimal medium, to a fermenting strain with productivities 0.25-0.5 g/L-1h-1 and 84-78% of CE, respectively and 90% of total conversions to the products. The findings in metabolic engineering here may release the limitations of utilizing glycerol in several eco-friendly biorefinery approaches. IMPORTANCEWith the avenues for achieving efficient lignocellulosic biorefinery scenarios, glycerol gained keen attention as an eco-friendly biomass-derived solvent for enhancing the dissociation of lignin and cell wall polysaccharides during pretreatment process. Co-fermentation of glycerol with the released sugars from biomass after the glycerolysis expands the resource for ethanol production and release from the burden of component separation. Titer productivities are one of the main obstacles for industrial applications of this process. Therefore, the generation of highly efficient glycerol fermenting yeast significantly promotes the applicability of the integrated biorefineries scenario. Besides, the glycerol is an important carbon resource for producing chemicals. Hence, the metabolic flux control of yeast from glycerol contributes to generation of cell factory producing chemicals from glycerol, promoting the association between biodiesel and bioethanol industries. Thus, this study will shed light on solving the problems of global warming and agricultural wastes, leading to establishment of the sustainable society.

Bacterial cellulose (BC) is an extracellular polysaccharide with myriad unique properties, such as high purity, water-holding capacity and biocompatibility, making it attractive in materials science. However, genetic engineering techniques for BC-producing microorganisms are rare. Herein, the electroporation-based gene transformation and the {lambda} Red-mediated gene knockout method with a nearly 100% recombination efficiency were established in the fast-growing and BC hyperproducer Enterobacter sp. FY-07. This genetic manipulation toolkit was validated by inactivating the protein subunit BcsA in the cellulose synthase complex. Subsequently, the inducible BC-producing strains from glycerol were constructed through inducible expression of the key gene fbp in the gluconeogenesis pathway, which recovered more than 80% of the BC production. Finally, the BC properties analysis results indicated that the induced-synthesized BC pellicles were looser, more porous and reduced crystallinity, which could further broaden the application prospects of BC. To our best knowledge, this is the first attempt to construct the completely inducible BC-producing strains. Our work paves the way for increasing BC productivity by metabolic engineering and broadens the available fabrication methods for BC-based advanced functional materials.

Rhodosporidium toruloides has emerged as a prominent candidate for producing single-cell oil from cost-effective feedstocks. In this study, the capability of R. toruloides to produce punicic acid (PuA), a representative plant unusual fatty acid, was investigated. The introduction of acyl lipid desaturase and conjugase (PgFADX) allowed R. toruloides to accumulate 3.7% of total fatty acids as PuA. Delta-12 acyl lipid desaturase (PgFAD2) and diacylglycerol acyltransferase 2 were shown to benefit PuA production. The strain with PgFADX and PgFAD2 coexpression accumulated 12% of its lipids as PuA from glucose, which translated into a PuA titer of 451.6 mg/L in shake flask condition. Utilizing wood hydrolysate as the feedstock, this strain produced 6.4% PuA with a titer of 310 mg/L. Taken together, the results demonstrated that R. toruloides could serve as an ideal platform for the production of plant-derived high-value conjugated fatty acid using agricultural and forestry waste as feedstock.

Besides the pledges for expanding uses of biofuels to sustain the humanosphere, abruptly massive needs emerged for sanitizers with turns COVID-19 to a pandemic. Therefore, ethanol is topping the social-demanding, although the three generations of production, from molasses/starch, lignocelluloses, and algae. Owing to the limited-availability of fermentable sugars from these resources, we addressed glycerol as a fourth bio-based carbon resource from biodiesel, soap, and fatty acid industries, which considers as a non-applicable source for bioethanol production. Here, we show the full strategy to generate efficient glycerol fermenting yeast by innovative rewriting the oxidation of cytosolic nicotinamide-adenine-dinucleotide (NADH) by O2-dependent dynamic shuttle while abolishing glycerol biosynthesis route. Besides, imposing a vigorous glycerol-oxidative pathway, the engineered strain demonstrated a breakthrough in conversion efficiency (up to 98%). Its capacity extending to produce up to 90g /l ethanol and > 2 g 1-1 h-1, which promoting the industrial view. Visionary metabolic engineering here provides horizons for further tremendous economic and health benefits with assuring for its enhancing for the other scenarios of biorefineries. SummaryEfficiently fermenting glycerol in yeast was developed by comprehensive engineering the glycerol pathways and rewriting NADH pathways.