Industrial Ethanol Production Research Articles

Assessment for industrial production of poplar ethanol after analysis of influencing factors and predicted yield

Assessment for industrial production of poplar ethanol after analysis of influencing factors and predicted yield

Optimal trade-off between boosted tolerance and growth fitness during adaptive evolution of yeast to ethanol shocks

BackgroundThe selection of Saccharomyces cerevisiae strains with higher alcohol tolerance can potentially increase the industrial production of ethanol fuel. However, the design of selection protocols to obtain bioethanol yeasts with higher alcohol tolerance poses the challenge of improving industrial strains that are already robust to high ethanol levels. Furthermore, yeasts subjected to mutagenesis and selection, or laboratory evolution, often present adaptation trade-offs wherein higher stress tolerance is attained at the expense of growth and fermentation performance. Although these undesirable side effects are often associated with acute selection regimes, the utility of using harsh ethanol treatments to obtain robust ethanologenic yeasts still has not been fully investigated.ResultsWe conducted an adaptive laboratory evolution by challenging four populations (P1–P4) of the Brazilian bioethanol yeast, Saccharomyces cerevisiae PE-2_H4, through 68–82 cycles of 2-h ethanol shocks (19–30% v/v) and outgrowths. Colonies isolated from the final evolved populations (P1c–P4c) were subjected to whole-genome sequencing, revealing mutations in genes enriched for the cAMP/PKA and trehalose degradation pathways. Fitness analyses of the isolated clones P1c–P3c and reverse-engineered strains demonstrated that mutations were primarily selected for cell viability under ethanol stress, at the cost of decreased growth rates in cultures with or without ethanol. Under this selection regime for stress survival, the population P4 evolved a protective snowflake phenotype resulting from BUD3 disruption. Despite marked adaptation trade-offs, the combination of reverse-engineered mutations cyr1A1474T/usv1Δ conferred 5.46% higher fitness than the parental PE-2_H4 for propagation in 8% (v/v) ethanol, with only a 1.07% fitness cost in a culture medium without alcohol. The cyr1A1474T/usv1Δ strain and evolved P1c displayed robust fermentations of sugarcane molasses using cell recycling and sulfuric acid treatments, mimicking Brazilian bioethanol production.ConclusionsOur study combined genomic, mutational, and fitness analyses to understand the genetic underpinnings of yeast evolution to ethanol shocks. Although fitness analyses revealed that most evolved mutations impose a cost for cell propagation, combination of key mutations cyr1A1474T/usv1Δ endowed yeasts with higher tolerance for growth in the presence of ethanol. Moreover, alleles selected for acute stress survival comprising the P1c genotype conferred stress tolerance and optimal performance under conditions simulating the Brazilian industrial ethanol production.

Ethanol production from cassava peels using Saccharomyces cerevisiae via ethanologenic fermentation process

PurposeThis study aims to assess the effect of water variation on bioethanol production from cassava peels (CP) using Saccharomyces cerevisiae yeast as the ethanologenic agent.Design/methodology/approachThe milled CP was divided into three treatment groups in a small-scale flask experiment where each 20 g CP was subjected to two-stage hydrolysis. Different amount of water was added to the fermentation process of CP. The fermented samples were collected every 24 h for various analyses.FindingsThe results of the fermentation revealed that the highest ethanol productivity and fermentation efficiency was obtained at 17.38 ± 0.30% and 0.139 ± 0.003 gL−1 h−1. The study affirmed that ethanol production was increased for the addition of water up to 35% for the CP hydrolysate process.Practical implicationsThe finding of this study demonstrates that S. cerevisiae is the key player in industrial ethanol production among a variety of yeasts that produce ethanol through sugar fermentation. In order to design truly sustainable processes, it should be expanded to include a thorough analysis and the gradual scaling-up of this process to an industrial level.Originality/valueThis paper is an original research work dealing with bioethanol production from CP using S. cerevisiae microbe.HighlightsHydrolysis of cassava peels using 13.1 M H2SO4 at 100 oC for 110 min gave high Glucose productivityHighest ethanol production was obtained at 72 h of fermentation using Saccharomyces cerevisiaeOptimal bioethanol concentration and yield were obtained at a hydration level of 35% agitationHighest ethanol productivity and fermentation efficiency were 17.3%, 0.139 g.L−1.h−1

ArcelorMittal announces the first industrial production of ethanol

ArcelorMittal announces the first industrial production of ethanol

Osmotic Stress Alleviation in Saccharomyces cerevisiae for High Ethanol Fermentations with Different Wort Substrates

High-gravity fermentation, used for ethanol production from sugarcane, corn, and mixed substrates, offers several benefits. Yeast, a rapidly multiplying unicellular microorganism, can be adapted for high sugar and ethanol tolerance on a lab scale. However, different substrates can enhance fermentation efficiency. Our study consisted of two experiments. In the first, we compared simple batch feeding with a fed-batch system for yeast selection in high-gravity fermentation. We ran eight cycles with increasing initial sugar contents (50 to 300 g L−1). No significant differences were observed in the first seven cycles, but in the eighth, the fed-batch system showed lower glycerol and fructose contents and higher cell viability than the simple batch system. In the second experiment, we used the fed-batch system with 300 g L−1 from sugarcane, corn, and mixed wort. The results showed that mixed wort produced higher ethanol contents and greater fermentation efficiency compared to corn and sugarcane as substrates. In conclusion, our findings indicate that the fed-batch system is more suitable for high-gravity fermentation on a lab scale, and the combination of sugarcane juice and corn can enhance fermentation efficiency, paving the way for integrating these substrates in industrial ethanol production.

Enhanced ethanol production using hydrophobic resin detoxified Pine forest litter hydrolysate and integrated fermentation process development supplementing molasses.

Globally escalating ethanol demand necessitates the use of hybrid technologies integrating first- and second-generation biofuel feedstocks for achieving the futuristic targets of gasoline replacement with bioethanol. In present study, an optimized two-step sequential pre-treatment (first dilute alkali, then dilute acid) of Pine forest litter (PFL) was developed. Furthermore, the saccharification of pre-treated PFL was optimized through Response Surface Methodology using Box-Behnken Design, wherein 0.558g/g of reducing sugar was released under the optimized conditions (12.5% w/v of biomass loading, 10 FPU/g of PFL enzyme loading, 0.15% v/v Tween-80 and 48h incubation time). Moreover, during hydrolysate fermentation using Saccharomyces cerevisiae NCIM 3288 strain, 22.51 ± 1.02g/L ethanol was produced. Remarkably, hydrophobic resin (XAD-4) treatment of PFL hydrolysate, significantly removed inhibitors (Furfural, 5-hydroxymethylfurfural and phenolics) and increased ethanol production to 27.38 ± 1.18g/L. Furthermore, during fermentation of molasses supplemented PFL hydrolysate (total initial sugar: 100 ± 3.27g/L), a maximum of 46.02 ± 2.08g/L ethanol was produced with 0.482g/g yield and 1.92g/l/h productivity. These findings indicated that the integration of molasses to lignocellulosic hydrolysate, would be a promising hybrid technology for industrial ethanol production within existing bio-refinery infrastructure.

Co-cultivation of Saccharomyces cerevisiae strains combines advantages of different metabolic engineering strategies for improved ethanol yield

Glycerol is the major organic byproduct of industrial ethanol production with the yeast Saccharomyces cerevisiae. Improved ethanol yields have been achieved with engineered S. cerevisiae strains in which heterologous pathways replace glycerol formation as the predominant mechanism for anaerobic re-oxidation of surplus NADH generated in biosynthetic reactions. Functional expression of heterologous phosphoribulokinase (PRK) and ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) genes enables yeast cells to couple a net oxidation of NADH to the conversion of glucose to ethanol. In another strategy, NADH-dependent reduction of exogenous acetate to ethanol is enabled by introduction of a heterologous acetylating acetaldehyde dehydrogenase (A-ALD). This study explores potential advantages of co-cultivating engineered PRK-RuBisCO-based and A-ALD-based strains in anaerobic bioreactor batch cultures. Co-cultivation of these strains, which in monocultures showed reduced glycerol yields and improved ethanol yields, strongly reduced the formation of acetaldehyde and acetate, two byproducts that were formed in anaerobic monocultures of a PRK-RuBisCO-based strain. In addition, co-cultures on medium with low acetate-to-glucose ratios that mimicked those in industrial feedstocks completely removed acetate from the medium. Kinetics of co-cultivation processes and glycerol production could be optimized by tuning the relative inoculum sizes of the two strains. Co-cultivation of a PRK-RuBisCO strain with a Δgpd1 Δgpd2 A-ALD strain, which was unable to grow in the absence of acetate and evolved for faster anaerobic growth in acetate-supplemented batch cultures, further reduced glycerol formation but led to extended fermentation times. These results demonstrate the potential of using defined consortia of engineered S. cerevisiae strains for high-yield, minimal-waste ethanol production.

Recovery and characterization of cellulosic ethanol from fermentation of sugarcane bagasse

Industrial production of ethanol by fermentation using renewable feedstock such as sugarcane stalks has been demonstrated as a sustainable fuel chain in Brazil. This work focused on the production of cellulosic ethanol from sugarcane bagasse in a pilot scale unit by applying the current bioprocessing strategies with the aim of recovering and characterizing the end products. The feedstock was pretreated at 190 °C and a residence time of 10 min. Enzymatic hydrolysis was performed with commercial cellulolytic enzymes. Fermentation’s substrates were formulated with hydrolysate and supplemented with 8%wt sugarcane molasses. The fermentations were set up to mimic the conventional industrial fermentation in Brazil’s ethanol distilleries at high cell density with cell recycling. The fermentation resulted in a reproducible performance by the yield of 0.49 g/g, productivity of 6.96 g/(L∙h), and cell viability of 95.3%. Ethanol was recovered in a lab-scale distillation batch system. Distilled fractions showed higher content of higher alcohols and sulfur content than the standard specification of ANP (National Agency of Petroleum - Brazilian Agency) for ethanol fuel. The distillation bottom product (vinasse) presented most characteristics suitable for fertilizer or biogas applications, except for sodium and sulfate content. Therefore, for a successful technology, transference processing adjustments should be made to make the product commercially suitable and the side stream compatible for disposal as fertilizer or digestion for biogas production.

Quantification and mitigation of byproduct formation by low-glycerol-producing Saccharomyces cerevisiae strains containing Calvin-cycle enzymes

BackgroundAnaerobic Saccharomyces cerevisiae cultures require glycerol formation to re-oxidize NADH formed in biosynthetic processes. Introduction of the Calvin-cycle enzymes phosphoribulokinase (PRK) and ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) has been shown to couple re-oxidation of biosynthetic NADH to ethanol production and improve ethanol yield on sugar in fast-growing batch cultures. Since growth rates in industrial ethanol production processes are not constant, performance of engineered strains was studied in slow-growing cultures.ResultsIn slow-growing anaerobic chemostat cultures (D = 0.05 h−1), an engineered PRK/RuBisCO strain produced 80-fold more acetaldehyde and 30-fold more acetate than a reference strain. This observation suggested an imbalance between in vivo activities of PRK/RuBisCO and formation of NADH in biosynthesis. Lowering the copy number of the RuBisCO-encoding cbbm expression cassette from 15 to 2 reduced acetaldehyde and acetate production by 67% and 29%, respectively. Additional C-terminal fusion of a 19-amino-acid tag to PRK reduced its protein level by 13-fold while acetaldehyde and acetate production decreased by 94% and 61%, respectively, relative to the 15 × cbbm strain. These modifications did not affect glycerol production at 0.05 h−1 but caused a 4.6 fold higher glycerol production per amount of biomass in fast-growing (0.29 h−1) anaerobic batch cultures than observed for the 15 × cbbm strain. In another strategy, the promoter of ANB1, whose transcript level positively correlated with growth rate, was used to control PRK synthesis in a 2 × cbbm strain. At 0.05 h−1, this strategy reduced acetaldehyde and acetate production by 79% and 40%, respectively, relative to the 15 × cbbm strain, without affecting glycerol production. The maximum growth rate of the resulting strain equalled that of the reference strain, while its glycerol production was 72% lower.ConclusionsAcetaldehyde and acetate formation by slow-growing cultures of engineered S. cerevisiae strains carrying a PRK/RuBisCO bypass of yeast glycolysis was attributed to an in vivo overcapacity of PRK and RuBisCO. Reducing the capacity of PRK and/or RuBisCO was shown to mitigate this undesirable byproduct formation. Use of a growth rate-dependent promoter for PRK expression highlighted the potential of modulating gene expression in engineered strains to respond to growth-rate dynamics in industrial batch processes.

Comparative evaluation of bioethanol fermentation process parameters using RSM, ANN and ANFIS

AbstractThe drive for renewable energy as an alternative to fossil fuel is on the increase globally. Modeling a renewable energy process is crucial for increasing process monitoring and control of plant efficiency for the ultimate objective of optimal biorefinery operations. This study aims to develop and compare models that best predict the fermentation process parameters of bioethanol production using corn‐steep liquor (CSL) as a media supplement. The response surface method (RSM), artificial neural networks (ANNs) and adaptive neuro‐fuzzy inference system (ANFIS) were tested in the modeling of bioethanol fermentation processes. Box–Behnken design was used to investigate fermentation process parameters considering the effect of CSL (0.5–5.5 w/v), pH (4, 5), time (12–36 h), temperature (25–35°C) and inoculum size (0.5–5.5 v/v). The results from the kinetics study show media formulation with corn steep liquor results in a comparable yield with that substituted with yeast extract. The study shows that, for CSL, a maximum ethanol concentration of 17.40 g L−1 was obtained after 48 h of fermentation while 21.53 g L−1 was attained after 6 h for the media formulation with yeast extract. Based on the model evaluation using statistical error indices, ANN predictability was better at R2 = 0.90; R = 0.95; SEP = 1.73. The ANN models described the process better than ANFIS and RSM. This study shows the intelligent predictive ability of ANN that could be useful for the scale‐up process of ethanol production in industry. © 2023 The Authors. Biofuels, Bioproducts and Biorefining published by Society of Industrial Chemistry and John Wiley & Sons Ltd.

Ethanol production using the whole solid-state fermented sugarcane bagasse cultivated by Trichoderma reesei RUT-C30 supplemented with commercial cellulase

Industrial ethanol production usually requires the costly use of commercial cellulase. Herein, we describe the direct use of cellulase produced by Trichoderma reesei RUT-C30 with sugarcane bagasse (SCB) as a substrate for the production of ethanol. The pretreated SCB supplemented with wheat bran (weight ratio of 4:1) was used for T. reesei cellulase production by solid-state fermentation. The cellulase activity titers of 5.5 ± 0.7 FPU/gdm was achieved. The activity increased to 15.0 ± 0.9 FPU/gdm when lactose was used as an inducer. The cellulase contained SCB (CSCB) was used directly as the raw material for ethanol production by Kluyveromyces marxianus at 40 °C, yielding 14.1 ± 1.8% (w/w) of ethanol. Supplementing 5 FPU/gdm of commercial cellulase (Cellic® CTec 2) to CSCB improved the ethanol yield to 30.3 ± 0.4% (w/w). Supplementing Cellic® CTec 2 provided large amount of β-glucosidase activity to CSCB, which hydrolyzes cellobiose to glucose, thereby preventing the inhibition of cellobiose to exoglucanase and endoglucanase. This study demonstrate the feasibility of integrating direct utilization of CSCB without further processing, conversion of CSCB to fermentable sugars, and fermentation of yeast to ethanol in a single reactor. This may be the most efficient way to convert biomass to valuable ethanol.

Moving towards the Application of Biocatalysis in Food Waste Biorefinery

Waste valorization is an important strategy to reduce environmental pollution and dependency on petroleum-based fuels. In this regard, utilization of food waste as a versatile and low-cost resource is important. Several advanced catalytic methods for the valorization of food waste have been widely investigated for the production of liquid biofuels. Along this line, chemical catalysts have been explored for the synthesis of liquid biofuels. Chemo-catalysis is mainly metal based, which requires harsh process conditions. Alternatively, biocatalysts are currently being investigated as a result of several advantages such as mild reaction conditions, recyclability, selectivity and biodegradability. In this work, recent biocatalytic technologies for the preparation of liquid biofuels through food waste valorization are discussed thoroughly. Lipases are employed for the synthesis of biodiesel and the upgradation of bio-oil, whereas methane mono-oxygenases could be explored for the production of methanol via the oxidation of methane generated from food wastes. Industrial production of ethanol from food waste using bioconversion technologies is a success story. To date, there has been no specific report on the use of food waste for propanol preparation using enzymes. The ABE process (Acetone–Butanol–Ethanol) (using suitable microorganisms) is used for butanol preparation, where the vacuum stripping system is integrated to remove butanol from the broth and circumvent inhibition. The synthesis of hydrocarbon fuels from fatty acids and triglycerides can be carried out using enzymes, such as carboxylic acid reductase and fatty acid photodecarboxylase (an algal photoenzyme). Both carboxylic acid reductase and fatty acid photodecarboxylase have not yet been applied in the direct valorization of food wastes. Furthermore, limitations of the reported methods, societal and economic aspects and a fresh perspective on the subject, along with important examples, are described.

Molecular Identification of Yeast Strains with High Fermentation Capacity Isolated from Kırkağaç Melon Varieties

The yield of fermentation process, bioethanol, is one of the important product obtained from renewable energy sources. Yeasts are commonly used in ethanol production due to their high ethanol tolerance, high ethanol productivity, and their ability to ferment different kinds of simple sugars. Saccharomyces cerevisiae yeast species is the most commonly used in industrial ethanol production. Therefore, isolation and identification of new yeast strains with high fermentation capacity is very important for the bioethanol industry. The aim of this study was isolation of novel and industrially applicable yeast species that can be used in bioethanol production. Yeast strains were isolated from the Dalaman, Altınbaş and Kıvırcık sarı dilim melon varieties that are unique to Kırkağaç district of Manisa province. The fermentation ability of yeast strains was evaluated and the selected yeast strains were identified by PCR-RFLP analysis of 26S and ITS1-5.8S-ITS2 rDNA gene regions. Sequence analysis of the 26S rDNA-D1/D2 gene region was used for molecular identification of yeast strains. The phylogenetic analysis of identified yeast strains was carried out using the MEGA XI phylogenetic analysis tool. It was determined that 14 of the 53 yeast strains isolated were able to ferment glucose and sucrose, and four of them were able to ferment lactose. The yeast strains having the fermentation capacity were identified as Pichia kluyverii, Lachancea thermotolerans, Pichia kudriavzevii, Saccharomyces cf. cerevisiae/paradoxus and Saccharomyces cerevisiae. These yeast strains have the potential to be used in the bioethanol industry after other physiological and biochemical tests are complete

Higher thermal and ethanol tolerance of a yeast strain isolated from oral cavity

Efficient bioethanol producing microorganisms must be endowed with peculiar physiological and technological traits, such as, higher thermal and ethanol tolerance. This encompasses a strain thermotolerance and an ability to grow at elevated sugar and ethanol concentration or ability to sustain dehydration process such as freeze drying. In this study, we characterized a thermotolerant yeast strain isolated from the human oral cavity regarding the above mentioned parameters. Such an uncommon niche was considered as the great potential reservoir, to isolate strains endowed with metabolic aptitudes requested for ethanol production. In the process, we have defined the YTerm-1strain ability to sustain high sugar and ethanol concentration that are two technological constrains in bioethanol production. Finally, we highlighted that the strain YTerm-1 was able to accumulate, at a high level, trehalose and β-glucan, two compounds conferring the cells an increased resistance to freeze drying process and osmotic stress. Our results suggest that the Yterm-1 strain showed a better growth ability and higher ethanol yield as compared to the industrial strain. Other metabolic traits, such as resistance to dehydration stress, tolerance to ethanol, accumulation of intracellular trehalose or membrane β-glucan confer to that isolate all the characteristics requested in industrial production of ethanol.

An engineered non-oxidative glycolytic bypass based on Calvin-cycle enzymes enables anaerobic co-fermentation of glucose and sorbitol by Saccharomyces cerevisiae

BackgroundSaccharomyces cerevisiae is intensively used for industrial ethanol production. Its native fermentation pathway enables a maximum product yield of 2 mol of ethanol per mole of glucose. Based on conservation laws, supply of additional electrons could support even higher ethanol yields. However, this option is disallowed by the configuration of the native yeast metabolic network. To explore metabolic engineering strategies for eliminating this constraint, we studied alcoholic fermentation of sorbitol. Sorbitol cannot be fermented anaerobically by S. cerevisiae because its oxidation to pyruvate via glycolysis yields one more NADH than conversion of glucose. To enable re-oxidation of this additional NADH by alcoholic fermentation, sorbitol metabolism was studied in S. cerevisiae strains that functionally express heterologous genes for ribulose-1,5-bisphosphate carboxylase (RuBisCO) and phosphoribulokinase (PRK). Together with the yeast non-oxidative pentose-phosphate pathway, these Calvin-cycle enzymes enable a bypass of the oxidative reaction in yeast glycolysis.ResultsConsistent with earlier reports, overproduction of the native sorbitol transporter Hxt15 and the NAD+-dependent sorbitol dehydrogenase Sor2 enabled aerobic, but not anaerobic growth of S. cerevisiae on sorbitol. In anaerobic, slow-growing chemostat cultures on glucose–sorbitol mixtures, functional expression of PRK-RuBisCO pathway genes enabled a 12-fold higher rate of sorbitol co-consumption than observed in a sorbitol-consuming reference strain. Consistent with the high Km for CO2 of the bacterial RuBisCO that was introduced in the engineered yeast strains, sorbitol consumption and increased ethanol formation depended on enrichment of the inlet gas with CO2. Prolonged chemostat cultivation on glucose–sorbitol mixtures led to loss of sorbitol co-fermentation. Whole-genome resequencing after prolonged cultivation suggested a trade-off between glucose-utilization and efficient fermentation of sorbitol via the PRK-RuBisCO pathway.ConclusionsCombination of the native sorbitol assimilation pathway of S. cerevisiae and an engineered PRK-RuBisCO pathway enabled RuBisCO-dependent, anaerobic co-fermentation of sorbitol and glucose. This study demonstrates the potential for increasing the flexibility of redox-cofactor metabolism in anaerobic S. cerevisiae cultures and, thereby, to extend substrate range and improve product yields in anaerobic yeast-based processes by enabling entry of additional electrons.

Variation in glucose metabolism under acidified sodium nitrite mediated nitrosative stress in Saccharomyces cerevisiae.

The work aimed to understand the important changes during glucose metabolism in Saccharomyces cerevisiae under acidified sodium nitrite (ac.NaNO2 ) mediated nitrosative stress. Confocal microscopy and fluorescence-activated cell sorting analysis were performed to investigate the generation of reactive nitrogen and oxygen species, and redox homeostasis under nitrosative stress was also characterized. Quantitative PCR analysis revealed that the expression of ADH genes was upregulated under such condition, whereas the ACO2 gene was downregulated. Some of the enzymes of the tricarboxylic acid cycle were partially inhibited, whereas malate metabolism and alcoholic fermentation were increased under nitrosative stress. Kinetics of ethanol production was also characterized. A network analysis was conducted to validate our findings. In the presence of ac.NaNO2 , in vitro protein tyrosine nitration formation was checked by western blotting using pure alcohol dehydrogenase and aconitase. Alcoholic fermentation rate was increased under stress condition and this altered metabolism might be conjoined with the defence machinery to overcome the nitrosative stress. This is the first work of this kind where the role of metabolism under nitrosative stress has been characterized in S. cerevisiae and it will provide a base to develop an alternative method of industrial ethanol production.

CRISPR-Cas9 Approach Constructed Engineered Saccharomyces cerevisiae with the Deletion of GPD2, FPS1, and ADH2 to Enhance the Production of Ethanol.

Bioethanol plays an important value in renewable liquid fuel. The excessive accumulation of glycerol and organic acids caused the decrease of ethanol content in the process of industrial ethanol production. In this study, the CRISPR-Cas9 approach was used to construct S. cerevisiae engineering strains by the deletion of GPD2, FPS1, and ADH2 for the improvement of ethanol production. RNA sequencing and transcriptome analysis were used to investigate the effect of gene deletion on gene expression. The results indicated that engineered S. cerevisiae SCGFA by the simultaneous deletion of GPD2, FPS1, and ADH2 produced 23.1 g/L ethanol, which increased by 0.18% in comparison with the wild-type strain with 50 g/L of glucose as substrate. SCGFA strain exhibited the ethanol conversion rate of 0.462 g per g of glucose. In addition, the contents of glycerol, lactic acid, acetic acid, and succinic acid in SCGFA decreased by 22.7, 12.7, 8.1, 19.9, and 20.7% compared with the wild-type strain, respectively. The up-regulated gene enrichment showed glycolysis, fatty acid, and carbon metabolism could affect the ethanol production of SCGFA according to the Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis. Therefore, the engineering strain SCGFA had great potential in the production of bioethanol.

Productivity of sweet potato (Ipomoea batatas L.) in the conditions of the RF CRNZ

The results of sweet potato yield in the climatic and soil conditions of the Non-Chernozem zone are presented, which allow to recommend the expansion of the areas of valuable crops to ensure the industrial production of flour, starch, ethanol, and raw materials for semi-finished products. Due to its origin from a warm subtropical climate, it requires appropriate temperature conditions and humidity, especially in May, when there is a high risk of spring frostsю Therefore, an assessment of growing technology under cover for the total and commercial yield of tubers of six sweet potato varieties was carried out. In the conditions of the Non-Chernozem zone of Russia, the sweet potato samples Sukhumskiy (yield 21.7 t/ha), Amsterdamskiy (24.8 t/ha), and Jewel variety (23.4 t/ha) showed high productivity on average over 2 years. Under experimental conditions, a change in the growth rate was noted depending on changes in agro-climatic conditions, while periods of growth stoppage under unfavorable conditions (drought) and periods of continued growth, which subsequently caused deformation of tubers (especially in the Pobeda 100 sample) were noted. The rate of increase in the mass of tubers showed a positive correlation with the amount of precipitation.

Metabolomic profiling of Spathaspora passalidarum fermentations reveals mechanisms that overcome hemicellulose hydrolysate inhibitors.

Understanding the mechanisms involved in tolerance to inhibitors is the first step in developing robust yeasts for industrial second-generation ethanol (E2G) production. Here, we used ultra-high-performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) and MetaboAnalyst 4.0 for analysis of MS data to examine the changes in the metabolic profile of the yeast Spathaspora passalidarum during early fermentation of hemicellulosic hydrolysates containing high or low levels of inhibitors (referred to as control hydrolysate or CH and strategy hydrolysate or SH, respectively). During fermentation of SH, the maximum ethanol production was 16g L-1 with a yield of 0.28gg-1 and productivity of 0.22g L-1h-1, whereas maximum ethanol production in CH fermentation was 1.74g L-1 with a yield of 0.11gg-1 and productivity of 0.01g L-1h-1. The high level of inhibitors in CH induced complex physiological and biochemical responses related to stress tolerance in S. passalidarum. This yeast converted compounds with aldehyde groups (hydroxymethylfurfural, furfural, 4-hydroxybenzaldehyde, syringaldehyde, and vanillin) into less toxic compounds, and inhibitors were found to reduce cell viability and ethanol production. Intracellularly, high levels of inhibitors altered the energy homeostasis and redox balance, resulting in lower levels of ATP and NADPH, while that of glycolytic, pentose phosphate, and tricarboxylic acid (TCA) cycle pathways were the most affected, being the catabolism of glucogenic amino acids, the main cellular response to inhibitor-induced stress. This metabolomic investigation reveals interesting targets for metabolic engineering of ethanologenic yeast strains tolerant against multiple inhibitors for E2G production. KEY POINTS: • Inhibitors in the hydrolysates affected the yeast's redox balance and energy status. • Inhibitors altered the glycolytic, pentose phosphate, TCA cycle and amino acid pathways. • S. passalidarum converted aldehyde groups into less toxic compounds.

Lime pretreatment of pelleted corn stover boosts ethanol titers and yields without water washing or detoxifying pretreated biomass

Large-scale industrial cellulosic ethanol production is significantly restricted by the high costs of lignocellulosic biomass handling, transportation and storage. Therefore, biomass densification is thought to be necessary to solve these logistical problems. Nevertheless, because of its high density, densified biomass may have an impact on subsequent biomass processing. In this study, lime pretreatment was investigated on pelleted corn stover (PCS) for ethanol production. The glucan and xylan conversions of lime-PCS exceeded 90% via enzymatic hydrolysis after optimization of pretreatment conditions. Corn stover was characterized using the flourier transform infrared spectrum (FT-IR) and scanning electron microscopy (SEM), which revealed that after lime pretreatment, the acetyl groups in biomass were removed and cell wall decomposition products redeposited on outer cell wall surfaces. Finally, without washing or detoxifying pretreated biomass, enzymatic hydrolysis and fermentation resulted in a high ethanol titer (65.1 g/L). The results indicated that lime pretreatment is efficient in pretreating PCS.