Efficient Ethanol Production Research Articles

Potencialidades del bagazo para la obtención de etanol frente a la generación de electricidad

The procedure to carry out the energy balance for ethanol production by bagasse's hydrolysis is presented. The loss of potentialities for electric power generation when bagasse is used to produce ethanol instead of electricity directly is calculated. Potential losses are 45-64% according to the efficiency of the lignocellulosic ethanol production. The relationship that exists between the volume of ethanol and the efficiency of Otto and Rankine cycles is analyzed. Those cycles are used to produce electricity from ethanol and bagasse, respectively.

Precipitate obtained following membrane separation of hydrothermally pretreated rice straw liquid revealed by 2D NMR to have high lignin content.

BackgroundHydrothermal pretreatment of lignocellulosic biomass such as rice straw can dissolve part of the lignin and hemicellulose into a liquid fraction, thus facilitating enzyme accessibility to cellulose in bioethanol production process. Lignin is awaited to be recovered after hydrothermal pretreatment for utilization as value-added chemical, and lignin recovery also means removal of fermentation inhibitors. To recover lignin with high content from the liquid fraction, it is necessary to separate lignin and hemicellulose-derived polysaccharide. Therefore, the following processes were applied: membrane separation with nanofiltration (NF) and enzymatic hydrolysis by hemicellulase. To clarify lignin-concentrated fraction obtained during these processes, the fates of lignin and polysaccharide components were pursued by a solution NMR method and confirmed by compositional analysis of each fraction.ResultsAfter hydrothermal pretreatment of rice straw, the NF concentrate of the supernatant of liquid fraction was hydrolyzed by hemicellulase and the resulting black precipitate was recovered. In this black precipitate, the intensity of NMR spectra related to lignin aromatic regions increased and those related to polysaccharides decreased, compared to rice straw, the solid fraction after hydrothermal pretreatment, and the NF concentrate. The lignin content of the black precipitate was 65.8 %. Lignin in the black precipitate included 52.9 % of the acid-insoluble lignin and 19.4 % of the soluble lignin in the NF concentrate of supernatant of liquid fraction.ConclusionA precipitate with high lignin content was obtained from supernatants of the liquid fraction. These results suggested that precipitation of lignin was enhanced from concentrated mixtures of lignin and hemicellulosic polysaccharides by hydrolyzing the polysaccharides. Precipitation of lignin can contribute to lignin recovery from lignocellulosic biomass and, at the same time, allow more efficient ethanol production in the subsequent fermentation process.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-015-0273-4) contains supplementary material, which is available to authorized users.

Efficient ethanol production from dried oil palm trunk treated by hydrothermolysis and subsequent enzymatic hydrolysis.

BackgroundOil palm trunk (OPT) is a valuable bioresource for the biorefinery industry producing biofuels and biochemicals. It has the distinct feature of containing a large amount of starch, which, unlike cellulose, can be easily solubilized by water when heated and hydrolyzed to glucose by amylolytic enzymes without pretreatment for breaking down the biomass recalcitrance. Therefore, it is suggested as beneficial to extract most of the starch from OPT through autoclaving and subsequent amylolytic hydrolysis prior to pretreatment. However, this treatment requires high capital and operational costs, and there could be a high probability of microbial contamination during starch processing. In terms of biochemical conversion of OPT, this study aimed to develop a simple and efficient ethanol conversion process without any chemical use such as acids and bases or detoxification.ResultsFor comparison with the proposed efficient ethanol conversion process, OPT was subjected to hydrothermal treatment at 180 °C for 30 min. After enzymatic hydrolysis of PWS, 43.5 g of glucose per 100 g dry biomass was obtained, which corresponds to 81.3 % of the theoretical glucose yield. Through subsequent alcohol fermentation, 81.4 % ethanol yield of the theoretical ethanol yield was achieved. To conduct the proposed new process, starch in OPT was converted to ethanol through enzymatic hydrolysis and subsequent fermentation prior to hydrothermal treatment, and the resulting slurry was subjected to identical processes that were applied to control. Consequently, a high-glucose yield of 96.3 % was achieved, and the resulting ethanol yield was 93.5 %.ConclusionsThe proposed new process was a simple method for minimizing the loss of starch during biochemical conversion and maximizing ethanol production as well as fermentable sugars from OPT. In addition, this methodology offers the advantage of reducing operational and capital costs due to minimizing the process for ethanol production by excluding expensive processes related to detoxification prior to enzymatic hydrolysis and fermentation such as washing/conditioning and solid–liquid separation of pretreated slurry. The potential future use of xylose-digestible microorganisms could further increase the ethanol yield from the proposed process, thereby increasing its effectiveness for the conversion of OPT into biofuels and biochemicals.

Utilization of recombinant Trichoderma reesei expressing Aspergillus aculeatus β-glucosidase I (JN11) for a more economical production of ethanol from lignocellulosic biomass

The capacity of Trichoderma reesei cellulase to degrade lignocellulosic biomass has been enhanced by the construction of a recombinant T.reesei strain expressing Aspergillus aculeatus β-glucosidase I. We have confirmed highly efficient ethanol production from converge-milled Japanese cedar by recombinant T.reesei expressing A.aculeatus β-glucosidase I (JN11). We investigated the ethanol productivity of JN11 and compared it with the cocktail enzyme T.reesei PC-3-7 with reinforced cellobiase activity by the commercial Novozyme 188. Results showed that the ethanol production efficiency under enzymatic hydrolysis of JN11 was comparable to the cocktail enzyme both on simultaneous saccharification and fermentation (SSF) or separate hydrolysis and fermentation (SHF) processes. Moreover, the cocktail enzyme required more protein loading for attaining similar levels of ethanol conversion as JN11. We propose that JN11 is an intrinsically economical enzyme that can eliminate the supplementation of BGL for PC-3-7, thereby reducing the cost of industrial ethanol production from lignocellulosic biomass.

Xylose fermentation by Saccharomyces cerevisiae using endogenous xylose-assimilating genes.

To genetically engineer Saccharomyces cerevisiae for improved ethanol productivity from glucose/xylose mixtures. An endogenous gene cassette composed of aldose reductase (GRE3), sorbitol dehydrogenase (SOR1) and xylulose kinase (XKS1) with a PGK1 promoter and a terminator was introduced into two S. cerevisiae strains, a laboratory strain (CEN.PK2-1C) and an industrial strain (Kyokai No. 7). The engineered Kyokai No. 7 strain (K7-XYL) exhibited a higher sugar consumption rate (1.03 g l(-1) h(-1)) and ethanol yield (63.8 %) from a glucose and xylose mixture compared to the engineered CEN.PK2-1C strain. Furthermore, K7-XYL produced a larger amount of ethanol (39.6 g l(-1)) compared to K7-SsXYL (32 g l(-1)) with integrated xylose reductase and xylitol dehydrogenase from a xylose-assimilating yeast Scheffersomyces stipitis instead of GRE3 and SOR1. The created S. cerevisiae strain showed sufficient xylose-fermenting ability to be used for efficient ethanol production from glucose/xylose.

Improvement of ethanol production from sweet sorghum juice under high gravity and very high gravity conditions: Effects of nutrient supplementation and aeration

Ethanol production by Saccharomyces cerevisiae NP 01 from sweet sorghum juice was conducted under nutrient supplementation and/or aeration conditions. Yeast extract (YE) and dried spent yeast (DSY) were used as nitrogen supplements. Under high gravity (HG, ∼200gl−1 of total sugar) conditions, the addition of either 6gl−1 of YE or 9gl−1 of DSY did not increase the ethanol concentration (P), but it promoted the rate of ethanol production or ethanol productivity (Qp). The Qp value of the control treatment (no supplement) was 1.96gl−1h−1. The P (93.4–94.0gl−1) and Qp (3.89–3.92gl−1h−1) values under the YE and DSY supplementation were comparable, indicating that DSY could be used to replace YE in ethanol production. Under very high gravity (VHG, ∼280gl−1 of total sugar) conditions, the supplementation of nitrogen and trace elements (Zn2+, Mg2+ and Mn2+) coupled with the aeration supply were required to improve the ethanol production efficiency. Under the supplementation (in gl−1) of DSY (13.5), Zn2+ (0.01), Mg2+ (0.05) and Mn2+ (0.04) in the presence of aeration supply at 0.05vvm for 12h, the P and Qp values were 126.3gl−1 and 2.11gl−1h−1, respectively. The P and Qp values under the same supplementation without aeration were 114.8gl−1 and 1.91gl−1h−1, respectively, and these values under no supplementation and no aeration were 108.0gl−1 and 1.50gl−1h−1, respectively. In addition, glycerol (the main by-product during ethanol fermentation) under aeration conditions was ∼3gl−1 lower than that without aeration.

Efficient ethanol production from inulin by two-stage aerate strategy

A major concern for ethanol production from inulin-containing materials, is the higher unconverted sugar, which increases the cost of ethanol production and wastewater treatment. Some key factors, such as inulinase, biomass or aeration rates, were studied to solve the problems in the process of ethanol fermentation from inulin. It was showed that more inulinase and increasing inoculum size can shorten the fermentation time, but could not reduce residual sugars. Two-stage aerate strategy was developed to utilize the remained sugars: keep the aeration at 5 h−1 at the first 12 h, and drop it to 1.2 h−1. Under this condition, contradiction between fermentation time and high ethanol yield was solved (60 h and 0.43 g g−1), and the final residual sugar concentration decreased to about 10 g L−1 with 98 g L−1 ethanol. The ethanol productivity was up to 1.63 g L−1 h−1, which is the highest productivity of ethanol fermentations from inulin-containing materials.

Dynamic flux balancing elucidates NAD(P)H production as limiting response to furfural inhibition in Saccharomyces cerevisiae.

Achieving efficient and economical lignocellulose-based bioprocess requires a robust organism tolerant to furfural, a major inhibitory compound present in lignocellulosic hydrolysate. The aim of this study was to develop a model that could generate quantitative descriptions of cell metabolism for elucidating the cell's adaptive response to furfural. Such a modelling tool could provide strategies for the design of more robust cells. A dynamic flux balance (dFBA) model of Saccharomyces cerevisiae was created by coupling a kinetic fermentation model with a previously published genome-scale stoichiometric model. The dFBA model was used for studying intracellular and extracellular flux responses to furfural perturbations under steady state and dynamic conditions. The predicted effects of furfural on dynamic flux profiles agreed well with previously published experimental results. The model showed that the yeast cell adjusts its metabolism in response to furfural challenge by increasing fluxes through the pentose phosphate pathway, TCA cycle, and proline and serine biosynthesis in order to meet the high demand of NAD(P)H cofactors. The model described here can be used to aid in systematic optimization of the yeast, as well as of the fermentation process, for efficient lignocellulosic ethanol production.

Efficient ethanol production from potato and corn processing industry waste using E. coli engineered to express Vitreoscilla haemoglobin

Engineering of ethanologenic E. coli to express the haemoglobin (VHb) from the bacterium Vitreoscilla has been shown to enhance ethanol production by fermentation of pure sugars, sugars from hydrolysis of lignocellulose, components of whey, and sugars from wastewater produced during potato processing. Here, these studies were extended to see whether the same effect could be seen when a mixture of waste materials from processing of potatoes and corn into potato and corn chips were used as sugar sources. Consistent increases in ethanol production coincident with VHb expression were seen in shake flasks at both low aeration and high aeration conditions. The ethanol increases were due almost entirely to increases in the amount of ethanol produced per unit of cell mass. The VHb strategy for increasing fermentation to ethanol (and perhaps other valuable fermentation products) may be of general use, particularly regarding conversion of otherwise discarded materials into valuable commodities.

Effect of cell immobilization and pH on Scheffersomyces stipitis growth and fermentation capacity in rich and inhibitory media

Abstract Background A wide range of value-added products can potentially be produced by bioprocessing hardwood spent sulfite liquors (HSSLs) that are by-products of pulp and paper industry with a high pentose sugar content. However, besides sugars, HSSLs contain considerable amounts of sulfonated lignin derivatives and acetic acid that inhibit the metabolic activity of most microorganisms. Scheffersomyces stipitis is a yeast with high capacity to ferment the pentose sugar xylose under appropriate microaerophilic conditions but it has limited tolerance to HSSL inhibitors. In the present study, cultivations of suspended and immobilized S. stipitis were compared in terms of growth capacity and by-product formation using rich medium and HSSL to investigate whether the immobilization of cells in calcium alginate beads could be a protection against inhibitors while favoring the presence of microaerophilic conditions. Results Whereas cell immobilization clearly favored the fermentative metabolism in rich medium, pH control was found to play a more important role than cell immobilization on the ethanol production efficiency from bio-detoxified HSSL (bdHSSL), leading to an improvement of 1.3-fold on the maximum ethanol productivity than using suspended cells. When immobilization and pH control were applied simultaneously, the ethanol yield improved by 1.3-fold with unchanged productivity, reaching 0.26 g ethanol.(g glucose + xylose)−1. Analysis of the immobilized beads inside revealed that the cells had grown in the opposite direction of the cortex. Conclusions Immobilization and pH control at 5.5, when applied simultaneously, have a positive impact on the fermentative metabolism of S. stipitis, improving the ethanol production efficiency. For the first time light microscopic analysis of the beads suggested that the nutrient and mass transfer limitations played a more important role in the fermentation than a possible protective role against inhibitors.

METABOLIC ADAPTATION STRATEGY USING Zymomonas mobilis CP4 CELLS FOR THE PRODUCTION OF SECOND GENERATION ETHANOL

During the past few decades, considerable effort has been made to utilize agricultural and forest residues as biomass feedstock for the production of bioethanol as an alternative fuel. The bacterium Zymomonas mobilis was shown to be extremely attractive for the production of second-generation ethanol from glucose of the cellulose fraction due to its ability to uptake high amounts of this sugar, resulting in high ethanol productivity values. However, the wild-type strains are unable to metabolize xylose that arises from the hemicellulose fraction. Molecular biology techniques were incorporated to render the strain used in this study capable of fermenting xylose into ethanol and thus increase the efficiency of second-generation ethanol production. Thus, the aim of this study was to evaluate the performance of a recombinant strain of Z. mobilis in simultaneous saccharification and co-fermentation (SSCF) processes, in which the fermentation of both sugars (glucose and xylose) occurs in one step. Regarding the genetic transformation,the 1,565 kb Z. mobilis plasmid pZMO1 was chemically synthesized and cloned into a synthetic vector that contains the E. coli and Z. mobilis replication checkmark origin,the XI, XK, TAL, and TKL genes and tetracycline resistance. Metabolic adaptation was performed by transferring the recombinant strain to media containing increased xylose concentrations. Then, an experimental response surface methodology was used to evaluatethe addition of glucose and xylose with different concentrations, as well as the incorporation of hemicellulosic hydrolyzate in different proportions. The recombinant Z. mobilis CP4 strain reached 25 g/L ethanol, confirming that approximately 50% of this pentose was consumed in the SSCF process when using 30% solids, 20.5% hemicellulose hydrolysate, 10 mg/L tetracycline, an enzyme load of 25 FPU/g cellulignin, and 10% of the initial inoculum.Â

Simultaneous hydrogen and ethanol production from cascade utilization of mono-substrate in integrated dark and photo-fermentative reactor.

BackgroundIntegrating hydrogen-producing bacteria with complementary capabilities, dark-fermentative bacteria (DFB) and photo-fermentative bacteria (PFB), is a promising way to completely recover bioenergy from waste biomass. However, the current coupled models always suffer from complicated pretreatment of the effluent from dark-fermentation or imbalance between dark and photo-fermentation, respectively. In this work, an integrated dark and photo-fermentative reactor (IDPFR) was developed to completely convert an organic substrate into bioenergy.ResultsIn the IDPFR, Ethanoligenens harbinese B49 and Rhodopseudomonas faecalis RLD-53 were separated by a membrane into dark and photo chambers, while the acetate produced by E. harbinese B49 in the dark chamber could freely pass through the membrane into the photo chamber and serve as a carbon source for R. faecalis RLD-53. The hydrogen yield increased with increasing working volume of the photo chamber, and reached 3.38 mol H2/mol glucose at the dark-to-photo chamber ratio of 1:4. Hydrogen production by the IDPFR was also significantly affected by phosphate buffer concentration, glucose concentration, and ratio of dark-photo bacteria. The maximum hydrogen yield (4.96 mol H2/mol glucose) was obtained at a phosphate buffer concentration of 20 mmol/L, a glucose concentration of 8 g/L, and a ratio of dark to photo bacteria of 1:20. As the glucose and acetate were used up by E. harbinese B49 and R. faecalis RLD-53, ethanol produced by E. harbinese B49 was the sole end-product in the effluent from the IDPFR, and the ethanol concentration was 36.53 mmol/L with an ethanol yield of 0.82 mol ethanol/mol glucose.ConclusionsThe results indicated that the IDPFR not only circumvented complex pretreatments on the effluent in the two-stage process, but also overcame the imbalance of growth and metabolic rate between DFB and PFB in the co-culture process, and effectively enhanced cooperation between E. harbinense B49 and R. faecalis RLD-53. Moreover, simultaneous hydrogen and ethanol production were achieved by coupling E. harbinese B49 and R. faecalis RLD-53 in the IDPFR. According to stoichiometry, the hydrogen and ethanol production efficiencies were 82.67% and 82.19%, respectively. Therefore, IDPFR was an effective strategy for coupling DFB and PFB to fulfill efficient energy recovery from waste biomass.

Improvement of acetic acid tolerance of Saccharomyces cerevisiae using a zinc-finger-based artificial transcription factor and identification of novel genes involved in acetic acid tolerance.

Acetic acid is present in cellulosic hydrolysate as a potent inhibitor, and the superior acetic acid tolerance of Saccharomyces cerevisiae ensures good cell viability and efficient ethanol production when cellulosic raw materials are used as substrates. In this study, a mutant strain of S. cerevisiae ATCC4126 (Sc4126-M01) with improved acetic acid tolerance was obtained through screening strains transformed with an artificial zinc finger protein transcription factor (ZFP-TF) library. Further analysis indicated that improved acetic acid tolerance was associated with improved catalase (CAT) activity. The ZFP coding sequence associated with the improved phenotype was identified, and real-time RT-PCR analysis revealed that three of the possible genes involved in the enhanced acetic acidtolerance regulated by this ZFP-TF, namely YFL040W, QDR3, and IKS1, showed decreased transcription levels in Sc4126-M01 in the presence of acetic acid, compared to those in the control strain. Sc4126-M01 mutants having QDR3 and IKS1 deletion (ΔQDR3 and ΔIKS1) exhibited higher acetic acid tolerance than the wild-type strain under acetic acid treatment. Glucose consumption rate and ethanol productivity in the presence of 5g/L acetic acid were improved in the ΔQDR3 mutant compared to the wild-type strain. Our studies demonstrated that the synthetic ZFP-TF library can be used to improve acetic acid tolerance of S. cerevisiae and that the employment of an artificial transcription factor can facilitate the exploration of novel functional genes involved in stress tolerance of S. cerevisiae.

On-farm solid state simultaneous saccharification and fermentation of whole crop forage rice in wrapped round bale for ethanol production.

BackgroundIn an attempt to reduce environmental loading during ethanol production from cellulosic plant biomass, we have previously proposed an on-site solid state fermentation (SSF) method for producing ethanol from whole crops, which at the same time provides cattle feed without producing wastes. During the ensiling of freshly harvested plant biomass with cellulase and glucoamylase, the added yeast and lactic acid bacteria induced simultaneous saccharification and production of ethanol and lactic acid in hermetically sealed containers on-farm. In a previous study, laboratory-scale SSF (using 250 g of fresh rice crop biomass) yielded 16.9 weight % ethanol in dry matter (DM) after 20 days of incubation. In this study, the fermentation volume was scaled up to a normal-sized round bale and the fermentation process (ethanol concentrations of the products) was monitored. The ethanol produced was recovered and the recovery efficiency was evaluated.ResultsSSF tests with forage rice round bales using polyethylene-wrapped whole plant materials (cultivar Leaf Star, average of 125.2 kg dry weight) were monitored in the field without temperature control. They yielded 14.0 weight % ethanol and 2.9 weight % lactic acid in DM after six months of incubation, and the ethanol ratio in the bale remained stable for 14 months after processing. SSF tests with three different rice cultivars were conducted for three years. Ethanol recovery from a fermented whole bale (244 kg fresh matter (FM) containing about 12.4 kg ethanol) by one-step distillation using vacuum distillation equipment yielded 86.3% ethanol collected from distilled solution (107 kg of 10.0 weight % ethanol). In addition, an average of 1.65 kg ethanol in 40.8 kg effluent per bale was recovered. Relative nitrogen content was higher in SSF products than in silage made from the same plant material, indicating that fermentation residue, whose quality is stabilized by the lactic acid produced, can be used as cattle feed.ConclusionsWe have successfully demonstrated an efficient on-site ethanol production system with non-sterilized whole rice crop round bale. However, issues concerning the establishment of the ethanol recovery procedure on-site and evaluation of the fermentation residue as cattle feed have to be addressed.

A Promising Low Beta-Glucan Barley Mutation of m351 for Better Bioethanol Production Use

Bioethanol is an important liquid fuel complement. Barley is a potential alternative raw material for ethanol production because its by-product is a nutritious feed. The barley m351mutant, which has a mutation for low beta-glucan content, was tested for its ethanol production efficiency and feed fraction quality in a pilot fermentation experiment. Grain samples of m351 and the corresponding wild type of Harrington were either treated or untreated with beta-glucanase during the ethanol production process. Compared to the corresponding wild-type line, m351 produced the same amount of ethanol. More importantly, the feed fraction derived from the fermentation process showed 5 % more protein and 7 % less beta-glucan than that from the wild type, indicating that the feed fraction from m351 was more valuable. The experiments provided evidence that m351 is a useful genetic resource for developing barley cultivars for use in bioethanol production.

Effect of Reducing Sugar and Total Nitrogen to Ethanol Production from Molasses by Saccharomyces cerevisiae

Indonesia's oil production has declined, while demand for derivative products is increasing. Objective of this research are to understand effect of reducing sugar and total nitrogen variation to ethanol production and fermentation efficiency, cell viability, acidity, temperature, dissolved oxygen with molasses by Saccharomyces cerevisiae (SAF Instant). Step of this research consist of determination of reducing sugar, ethanol fermentation, total nitrogen determination, ethanol determination and data analysis. Treatment of reducing sugar (GR) and total nitrogen (N) (g.L -1 ) that are GR 100 N 0, GR 100 N 6, GR 100 N 10, GR 125 N 0, GR 125 N 6 and GR 125 N 10. Fermentation was carried out for 72 hours with three replications. Observation parameters every 24 hours are ethanol and reducing sugar concentration, temperature, acidity and dissolved oxygen. Highest ethanol resulted from GR 125 N 6 (3.68 g.L -1 ) and GR 100 N 6 (3.53 g.L -1 ). Low reducing sugar consumption inhibited by by-product of yeast metabolism and molasses chemical compound, lead leaves high sugar concentration (> 80 g.L -1 ). GR 100 N 6 and GR 125 N 6 have highest fermentation efficiency (69 and 57 %). There was no increase in temperature and decrease in pH significantly (α>0.05). Dissolved oxygen decreased significantly (α>0.05) at the early of fermentation and decrease until the end of fermentation. Total nitrogen 6 g g.L -1 has the highest fermentation efficiency. Keywords: ethanol, molasses, reducing sugar, Saccharomyces cerevisiae , total nitrogen

Genetic improvement of native xylose-fermenting yeasts for ethanol production.

Lignocellulosic substrates are the largest source of fermentable sugars for bioconversion to fuel ethanol and other valuable compounds. To improve the economics of biomass conversion, it is essential that all sugars in potential hydrolysates be converted efficiently into the desired product(s). While hexoses are fermented into ethanol and some high-value chemicals, the bioconversion of pentoses in hydrolysates remains inefficient. This remains one of the key challenges in lignocellulosic biomass conversion. Native pentose-fermenting yeasts can ferment both glucose and xylose in lignocellulosic biomass to ethanol. However, they perform poorly in the presence of hydrolysate inhibitors, exhibit low ethanol tolerance and glucose repression, and ferment pentoses less efficiently than the main hexoses glucose and mannose. This paper reviews classical and molecular strain improvement strategies applied to native pentose-fermenting yeasts for improved ethanol production from xylose and lignocellulosic substrates. We focus on Pachysolen tannophilus, Scheffersomyces (Candida) shehatae, Scheffersomyces (Pichia) stipitis, and Spathaspora passalidarum which are good ethanol producers among the native xylose-fermenting yeasts. Strains obtained thus far are not robust enough for efficient ethanol production from lignocellulosic hydrolysates and can benefit from further improvements.

Conversion of steam-exploded cedar into ethanol using simultaneous saccharification, fermentation and detoxification process

In this study, we investigated the simultaneous saccharification, fermentation and detoxification SSDF process of steam-exploded cedar using a detoxification microorganism, Ureibacillus thermosphaericus A1, to facilitate efficient ethanol production. Steam explosion was applied as a pretreatment before enzymatic saccharification followed by alcohol fermentation. The highest glucose conversion rate was observed in the sample pretreated with a steam pressure of 45atm for 5min. Alcohol production by a heat-tolerant yeast, Saccharomyces cerevisiae BA11, was inhibited strongly by inhibitory materials present in the steam-exploded cedar, such as formic acid, furfural, and 5-hydroxymethylfurfural. The maximum amount of ethanol, i.e., 0.155g ethanol/g dry steam-exploded cedar, which corresponded to 74% of the theoretical ethanol yield, was obtained using the SSDF when U. thermosphaericus A1 degraded the inhibitory materials. A fed batch SSDF culture, in which U. thermosphaericus A1 was used to maintain low concentrations of inhibitory materials, was effective for increasing the ethanol concentration.

Point mutation of H3/H4 histones affects acetic acid tolerance in Saccharomyces cerevisiae

The molecular mechanism of acetic acid tolerance in yeast remains unclear despite of its importance for efficient cellulosic ethanol production. In this study, we examined the effects of histone H3/H4 point mutations on yeast acetic acid tolerance by comprehensively screening a histone H3/H4 mutant library. A total of 24 histone H3/H4 mutants (six acetic acid resistant and 18 sensitive) were identified. Compared to the wild-type strain, the histone acetic acid-resistant mutants exhibited improved ethanol fermentation performance under acetic acid stress. Genome-wide transcriptome analysis revealed that changes in the gene expression in the acetic acid-resistant mutants H3 K37A and H4 K16Q were mainly related to energy production, antioxidative stress. Our results provide novel insights into yeast acetic acid tolerance on the basis of histone, and suggest a novel approach to improve ethanol production by altering the histone H3/H4 sequences.

Minimization of Bacterial Contamination with High Solid Loading during Ethanol Production from Lignocellulosic Materials

Ethanol is the most important renewable fuel in the transportation sector. Its production from lignocellulosic materials, commonly referred to as second generation ethanol, is considered more attractive than production from starch and sugar crops. Bacterial contamination by lactic acid-producing bacteria is still a major problem during ethanol production processes. Bacteria compete with the yeast by consuming the sugars and the nutrients required by the yeast for efficient ethanol production. This often causes substantial economic losses at industrial fermentations. In this study, without any sterilization of the substrate, simultaneous saccharification and fermentation (SSF) was performed using cellulase Cellic® Ctec2 enzyme for hydrolysis and Baker’s yeast, Saccharomyces cerevisiae, was used as the fermenting organism with different loads of suspended solids - 8%, 10% and 12%. With8%and 10% SS, there was a significant contamination, which caused consumption of both hexoses pentose sugars in the fermentation medium, this resulted in lactic acid concentrations of 43 g/L and 36 g/L from 10% SS and 8% SS respectively. In contrast, only 2.9 g/L lactic acid was observed with 12% SS. An ethanol concentration of 47 g/L was produced from high solid loading of 12% SS while just 26 g/L and 23 g/L were produced from 10% and 8% SS respectively. Our results show that SSF with 12% SS has an increased concentration of inhibitors, particularly acetic acid which selectively inhibited the bacterial growth without affecting the metabolic activities of the yeast during the fermentation.