High ethanol fermentation performance of the dry dilute acid pretreated corn stover by an evolutionarily adapted Saccharomyces cerevisiae strain

Cas9-Based Metabolic Engineering of Issatchenkia orientalis for Enhanced Utilization of Cellulosic Hydrolysates

Issatchenkia orientalis, exhibiting high tolerance against harsh environmental conditions, is a promising metabolic engineering host for producing fuels and chemicals from cellulosic hydrolysates containing fermentation inhibitors under acidic conditions. Although genetic tools for I. orientalis exist, they require auxotrophic mutants so that the selection of a host strain is limited. We developed a drug resistance gene (cloNAT)-based genome-editing method for engineering any I. orientalis strains and engineered I. orientalis strains isolated from various sources for xylose fermentation. Specifically, xylose reductase, xylitol dehydrogenase, and xylulokinase from Scheffersomyces stipitis were integrated into an intended chromosomal locus in four I. orientalis strains (SD108, IO21, IO45, and IO46) through Cas9-based genome editing. The resulting strains (SD108X, IO21X, IO45X, and IO46X) efficiently produced ethanol from cellulosic and hemicellulosic hydrolysates even though the pH adjustment and nitrogen source were not provided. As they presented different fermenting capacities, selection of a host I. orientalis strain was crucial for producing fuels and chemicals using cellulosic hydrolysates.

How adaptive laboratory evolution can boost yeast tolerance to lignocellulosic hydrolyses

The yeast Saccharomyces cerevisiae is an excellent candidate for establishing cell factories to convert lignocellulosic biomass into chemicals and fuels. To enable this technology, yeast robustness must be improved to withstand the fermentation inhibitors (e.g., weak organic acids, phenols, and furan aldehydes) resulting from biomass pretreatment and hydrolysis. Here, we discuss how evolution experiments performed in the lab, a method commonly known as adaptive laboratory evolution (ALE), may contribute to lifting yeast tolerance against the inhibitors of lignocellulosic hydrolysates (LCHs). The key is that, through the combination of whole-genome sequencing and reverse engineering, ALE provides a robust platform for discovering and testing adaptive alleles, allowing to explore the genetic underpinnings of yeast responses to LCHs. We review the insights gained from past evolution experiments with S. cerevisiae in LCH inhibitors and propose experimental designs to optimise the discovery of genetic variants adaptive to biomass toxicity. The knowledge gathered through ALE projects is envisaged as a roadmap to engineer superior yeast strains for biomass-based bioprocesses.

Spent mushroom substrates for ethanol production - Effect of chemical and structural factors on enzymatic saccharification and ethanolic fermentation of Lentinula edodes-pretreated hardwood

Spent mushroom substrates (SMS) from cultivation of shiitake (Lentinula edodes) on three hardwood species were investigated regarding their potential for cellulose saccharification and for ethanolic fermentation of the produced hydrolysates. High glucan digestibility was achieved during enzymatic saccharification of the SMSs, which was related to the low mass fractions of lignin and xylan, and it was neither affected by the relative content of lignin guaiacyl units nor the substrate crystallinity. The high nitrogen content in SMS hydrolysates, which was a consequence of the fungal pretreatment, was positive for the fermentation, and it ensured ethanol yields corresponding to 84-87% of the theoretical value in fermentations without nutrient supplementation. Phenolic compounds and acetic acid were detected in the SMS hydrolysates, but due to their low concentrations, the inhibitory effect was limited. The solid leftovers resulting from SMS hydrolysis and the fermentation residues were quantified and characterized for further valorisation.

Development of multiple inhibitor tolerant yeast via adaptive laboratory evolution for sustainable bioethanol production

The present research work aimed at developing robust yeast cell factory via adaptive laboratory evolution (ALE) for improved cellulosic bioethanol production. Kluyveromyces marxianus JKH5, a newly isolated thermotolerant ethanologenic yeast, was engineered by serial passaging for 60 generations in medium supplemented with gradually higher concentration of inhibitors (acetic acid, furfural, and vanillin) that are generated during dilute acid pretreatment. The improved strain K. marxianus JKH5 C60, showed 3.3-fold higher specific growth rate, 56% reduced lag phase and 80% enhanced fermentation efficiency at 42 °C in comparison to parent strain in inhibitor cocktail comprising medium. Bioethanol production by simultaneous saccharification and fermentation of sequential dilute acid-alkali pretreated sugarcane bagasse in presence of inhibitors, resulted in ethanol titre and yield, respectively, 54.8 ± 0.9 g/L and 0.40 g/g. The adapted yeast can be used to ferment unwashed pretreated biomass, thereby, reducing overall cost, time, and wastewater generation, hence making bioethanol production sustainable.

Fagonia arabica L.: A review of its phytochemistry, pharmacology and traditional uses

BACKGROUND

Fagonia arabica, belongs to family Zygophyllaceae, is a medicinal plant, widely distributed in the desert areas of the world including Saudi Arabia, Pakistan, India and South Africa. The present review aims to explore the published information on the traditional uses, ethnobotanical knowledge, phytochemistry and various biological activities like antioxidant, antimicrobial, thrombolytic activities and anticoagulant effects of Fagonia arabica with critical analysis on the gaps and future perspectives.

METHOD

A literature survey was performed by searching the digital libraries and the scientific databases including Scopus, Google Scholar, SciFinder, ACS, Web of Science and published books.

RESULTS

Fagonia arabica plant has been reported to have a wide range of traditional uses in sore mouth, smallpox, hematological, neurological, endocrinological, inflammatory, cooling agent in stomatitis, vertigo and endothermic reaction in the body. Several bioactive constituents including glycosides, flavonoids, terpenoids, saponins, alkaloids and trace elements were recorded from Fagonia arabica plant. The isolation and identification of two flavonoid glycosides (kaempferol-7-O-rhamnoside and acacetin-7-O-rhamnoside) were also reported. Fagonia arabica has been studied for its wide range of biological activities, which include antioxidant, antimicrobial, cardioprotective and anticoagulant.

CONCLUSION

It is apparent from the literature that Fagonia arabica plant possesses a wide range of medicinal and pharmacological uses and has been studied for its various pharmacological activities and medicinal applications. Critical analysis reveals that the plant has the huge potential for pharmaceutical and pharmacological applications.

Adaptive laboratory evolution principles and applications in industrial biotechnology

Adaptive laboratory evolution (ALE) is an innovative approach for the generation of evolved microbial strains with desired characteristics, by implementing the rules of natural selection as presented in the Darwinian Theory, on the laboratory bench. New as it might be, it has already been used by several researchers for the amelioration of a variety of characteristics of widely used microorganisms in biotechnology. ALE is used as a tool for the deeper understanding of the genetic and/or metabolic pathways of evolution. Another important field targeted by ALE is the manufacturing of products of (high) added value, such as ethanol, butanol and lipids. In the current review, we discuss the basic principles and techniques of ALE, and then we focus on studies where it has been applied to bacteria, fungi and microalgae, aiming to improve their performance to biotechnological procedures and/or inspect the genetic background of evolution. We conclude that ALE is a promising and efficacious method that has already led to the acquisition of useful new microbiological strains in biotechnology and could possibly offer even more interesting results in the future.

Overexpression of SFA1 in engineered Saccharomyces cerevisiae to increase xylose utilization and ethanol production from different lignocellulose hydrolysates

Here, an engineered Saccharomyces cerevisiae strain SFA1^OE was constructed by overexpressing SFA1 in a reported WXY70 with effective six-gene clusters. Under simulated maize hydrolysate, SFA1^OE produced an ethanol yield of 0.492 g/g totalsugars within 48 h. The productivity of SFA1^OE was comprehensively evaluated in typical hydrolysates from stalks of maize, sweet sorghum, wheat and Miscanthus. Within 48 h, SFA1^OE achieved an ethanol yield of 0.489 g/g totalsugars in the optimized hydrolysate of alkaline-distilled sweet sorghum bagasse derived from Advanced Solid-State Fermentation process. By crossing SFA1^OE with a DQ1-derived haploid strain, we obtained an evolved diploid strain SQ-2, exhibiting improved ethanol production and thermotolerance. This study demonstrates that overexpressing SFA1 enables efficient fermentation performance in different lignocellulosic hydrolysates, especially in the hydrolysate of alkaline-distilled sweet sorghum bagasse. The increased cellulosic bioethanol production of SFA1^OE provides a promising platform for efficient biorefineries.

Bioconversion of biomass waste into high value chemicals

Dwindling petroleum resources and increasing environmental concerns have stimulated the production of platform chemicals via biochemical processes through the use of renewable carbon sources. Various types of biomass wastes, which are biodegradable and vastly underutilized, are generated worldwide in huge quantities. They contain diverse chemical constituents, which may serve as starting points for the manufacture of a wide range of valuable bio-derived platform chemicals, intermediates, or end products via different conversion pathways. The valorization of inexpensive, abundantly available, and renewable biomass waste could provide significant benefits in response to increasing fossil fuel demands and manufacturing costs, as well as emerging environmental concerns. This review explores the potential for the use of available biomass waste to produce important chemicals, such as monosaccharides, oligosaccharides, biofuels, bioactive molecules, nanocellulose, and lignin, with a focus on commercially viable technologies.

High Gravity Fermentation of Sugarcane Bagasse Hydrolysate by Saccharomyces pastorianus to Produce Economically Distillable Ethanol Concentrations: Necessity of Medium Components Examined

A major economic obstacle in lignocellulosic ethanol production is the low sugar concentrations in the hydrolysate and subsequent fermentation to economically distillable ethanol concentrations. We have previously demonstrated a two-stage fermentation process that recycles xylose with xylose isomerase to increase ethanol productivity, where the low sugar concentrations in the hydrolysate limit the final ethanol concentrations. In this study, three approaches are combined to increase ethanol concentrations. First, the medium-additive requirements were investigated to reduce ethanol dilution. Second, methods to increase the sugar concentrations in the sugarcane bagasse hydrolysate were undertaken. Third, the two-stage fermentation process was recharacterized with high gravity hydrolysate. It was determined that phosphate and magnesium sulfate are essential to the ethanol fermentation. Additionally, the Escherichia coli extract and xylose isomerase additions were shown to significantly increase ethanol productivity. Finally, the fermentation on hydrolysate had only slightly lower productivity than the reagent-grade sugar fermentation; however, both fermentations had similar final ethanol concentrations. The present work demonstrates the capability to produce ethanol from high gravity sugarcane bagasse hydrolysate using Saccharomyces pastorianus with low yeast inoculum in minimal medium. Moreover, ethanol productivities were on par with pilot-scale commercial starch-based facilities, even when the yeast biomass production stage was included.

In-Depth Two-Stage Transcriptional Reprogramming and Evolutionary Engineering of Saccharomyces cerevisiae for Efficient Bioethanol Production from Xylose with Acetate

In order to achieve rapid xylose utilization in the presence of acetate, improved yeast strains were engineered for higher bioethanol production. First, a six-gene cluster, including XYL1/XYL2/XKS1/TAL1/PYK1/MGT05196, was generated by using an in-depth two-stage (glucose and xylose) transcription reprogramming strategy in an evolutionary adapted strain of CE7, resulting in two improved engineered strains WXY46 and WXY53. Through a combined screening of xylose and glucose stage-specific promoters between tricarboxylic acid (TCA)/HSP and constitutive types, respectively, WXY46 with the constitutive promoters showed a much higher ethanol yield than that of WXY53 with the TCA/HSP promoters. Second, an optimized strain WXY74 was obtained by using more copies of a six-gene cluster, which resulted in a higher ethanol yield of 0.500 g/g total sugars with acetate conditions. At last, simultaneous saccharification and co-fermentation were performed by using the evolved WXY74 strain, which produced 58.4 g/L of ethanol from wheat straw waste and outperformed previous haploid XR-XDH strains.

Transcriptomic analysis of the oleaginous yeast Lipomyces starkeyi during lipid accumulation on enzymatically treated corn stover hydrolysate

BACKGROUND

Efficient and economically viable production of biofuels from lignocellulosic biomass is dependent on mechanical and chemical pretreatment and enzymatic hydrolysis of plant material. These processing steps yield simple sugars as well as plant-derived and process-added organic acids, sugar-derived dehydration products, aldehydes, phenolics and other compounds that inhibit the growth of many microorganisms. Lipomyces starkeyi is an oleaginous yeast capable of robust growth on a variety of sugars and lipid accumulation on pretreated lignocellulosic substrates making it attractive as an industrial producer of biofuels. Here, we examined gene expression during batch growth and lipid accumulation in a 20-L bioreactor with either a blend of pure glucose and xylose or pretreated corn stover (PCS) that had been enzymatically hydrolyzed as the carbon sources.

RESULTS

We monitored sugar and ammonium utilization as well as biomass accumulation and found that growth of L. starkeyi is inhibited with PCS hydrolysate as the carbon source. Both acetic acid and furfural are present at concentrations toxic to L. starkeyi in PCS hydrolysate. We quantified gene expression at seven time-points for each carbon source during batch growth and found that gene expression is similar at physiologically equivalent points. Analysis of promoter regions revealed that gene expression during the transition to lipid accumulation is regulated by carbon and nitrogen catabolite repression, regardless of carbon source and is associated with decreased expression of the translation machinery and suppression of the cell cycle. We identified 73 differentially expressed genes during growth phase in the bioreactor that may be involved in detoxification of corn stover hydrolysate.

CONCLUSIONS

Growth of L. starkeyi is inhibited by compounds present in PCS hydrolysate. Here, we monitored key metabolites to establish physiologically equivalent comparisons during a batch bioreactor run comparing PCS hydrolysate and purified sugars. L. starkeyi's response to PCS hydrolysate is primarily at the beginning of the run during growth phase when inhibitory compounds are presumably at their highest concentration and inducing the general detoxification response by L. starkeyi. Differentially expressed genes identified herein during growth phase will aid in the improvement of industrial strains capable of robust growth on substrates containing various growth inhibitory compounds.

Biochemical engineering in China

Chinese biochemical engineering is committed to supporting the chemical and food industries, to advance science and technology frontiers, and to meet major demands of Chinese society and national economic development. This paper reviews the development of biochemical engineering, strategic deployment of these technologies by the government, industrial demand, research progress, and breakthroughs in key technologies in China. Furthermore, the outlook for future developments in biochemical engineering in China is also discussed.

A preliminary study on l-lysine fermentation from lignocellulose feedstock and techno-economic evaluation

l-Lysine is a commodity amino acid produced from starch feedstock. Various alternative feedstocks had been used for l-lysine production, but the yield was very low. This study took the first preliminary investigation on l-lysine production from lignocellulose for the replacement of food-crop starch. Corn stover was dry acid pretreated and biodetoxified, then used for enzymatic hydrolysis and l-lysine fermentation by an industrial Corynebacterium glutamicum strain. Various fermentation parameters, nutrient additions, and operation variables were applied and finally 33.8 g/L of l-lysine was obtained. This l-lysine titer is still below that of starch based fermentation, but already 3-5 folds greater than that of other alternative feedstocks based fermentation. A techno-economic analysis was conducted and the minimum selling price of l-lysine (hydrochloride form) was calculated to be $2.445 per kg. The cost reduction by the future improvement could fill the technical and economic gap between the cellulosic and starch based l-lysine production.

Ethylenediamine pretreatment of corn stover facilitates high gravity fermentation with low enzyme loading

This work investigated the effect of ethylenediamine pretreatment on reducing enzyme loading in high gravity fermentation. At optimal conditions of ethylenediamine pretreatment, 85.5% lignin was removed. Enzyme adsorption analysis using a fluorescent cellulose-binding protein showed 35.2% increase of productive adsorption of enzymes to ethylenediamine pretreated biomass, which was caused by high delignification and dramatically increased surface roughness and porosity. In SScF at 15% glucan loading, up to 82.2 g/L ethanol was achieved with a relatively low enzyme loading of 3.6 FPU/g dry matter. It suggested that the remarkably high digestibility of EDA pretreated corn stover could effectively reduce the enzyme loading in the high gravity fermentation of cellulosic ethanol.

Strategies for enhancing microbial tolerance to inhibitors for biofuel production: A review

Using lignocellulosic biomass for the production of renewable biofuel provides a sustainable and promising solution to the crisis of energy and environment. However, the processes of biomass pretreatment and biofuel fermentation bring a variety of inhibitors to microbial strains. These inhibitors repress microbial growth, decrease biofuel yields and increase fermentation costs. The production of biofuels from renewable lignocellulosic biomass relies on the development of tolerant and robust microbial strains. In recent years, the advancement of tolerance engineering and evolutionary engineering provides powerful platform for obtaining host strains with desired tolerance for further metabolic engineering of biofuel pathways. In this review, we summarized the inhibitors derived from biomass pretreatment and biofuel fermentation, the mechanisms of inhibitor toxicity, and the strategies for enhancing microbial tolerance.

An integrated process for xylooligosaccharide and bioethanol production from corncob

An integrated process for xylooligosaccharides (XOs) and bioethanol production from corncob was investigated. XOs were produced by a consecutive process of KOH treatment and hydrolysis by an in-house thermostable endo-xylanase from Streptomyces thermovulgaris. XO yields of 0.15 g/g_{KOH-treated corncob} (22.13 g/L) and 0.52 g/g_{raw corncob} of cellulose-rich corncob (CRC) were obtained. After 96 h of enzymatic hydrolysis, CRC hydrolysate contained 62.16, 51.21, 10.03 and 0.92 g/L of total sugar, glucose, xylose and arabinose, respectively. Bioethanol production by separate hydrolysis and fermentation (SHF) using CRC hydrolysate, and by simultaneous saccharification and fermentation (SSF) using CRC was studied at 40 °C for thermotolerant Candida glabrata. SHF showed an ethanol yield of 0.28 g/g_CRC (21.92 g/L) and ethanol productivity of 0.304 g/L/h with 93% theoretical yield. Surprisingly, by SSF, those parameters were 0.27 g/g_CRC (31.32 g/L), 0.33 g/L/h and 89%, respectively. This integrated process might be a new cost-effective approach for corncob valorization.

Optimization of cellulolytic enzyme components through engineering Trichoderma reesei and on-site fermentation using the soluble inducer for cellulosic ethanol production from corn stover

BACKGROUND

Cellulolytic enzymes produced by Trichoderma reesei are widely studied for biomass bioconversion, and enzymatic components vary depending on different inducers. In our previous studies, a mixture of glucose and disaccharide (MGD) was developed and used to induce cellulase production. However, the enzymatic profile induced by MGD is still not defined, and further optimization of the enzyme cocktail is also required for efficient ethanol production from lignocellulosic biomass.

RESULTS

In this study, cellulolytic enzymes produced by T. reesei Rut C30 using MGD and alkali-pretreated corn stover (APCS) as inducer were compared. Cellular secretome in response to each inducer was analyzed, which revealed a similar enzyme profile. However, significant difference in the content of cellulases and xylanase was detected. Although MGD induction enhanced β-glucosidase production, its activity was still not sufficient for biomass hydrolysis. To overcome such a disadvantage, aabgl1 encoding β-glucosidase in Aspergillus aculeatus was heterologously expressed in T. reesei Rut C30 under the control of the pdc1 promoter. The recombinant T. reesei PB-3 strain showed an improved β-glucosidase activity of 310 CBU/mL in the fed-batch fermentation, 71-folds higher than that produced by the parent strain. Meanwhile, cellulase activity of 50 FPU/mL was detected. Subsequently, the crude enzyme was applied for hydrolyzing corn stover with a solid loading of 20% through separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation, respectively, for ethanol production. Better performance was observed in the SHF process, through which a total of 119.9 g/L glucose was released within 12 h for concomitant ethanol production of 54.2 g/L.

CONCLUSIONS

The similar profile of cellulolytic enzymes was detected under the induction of MGD and APCS, but higher amount of cellulases was present in the crude enzyme induced by MGD. However, β-glucosidase activity induced by MGD was not sufficient for hydrolyzing lignocellulosic biomass. High titers of cellulases and β-glucosidase were achieved simultaneously by heterologous expression of aabgl1 in T. reesei and fed-batch fermentation through feeding MGD. We demonstrated that on-site cellulase production by T. reesei PB-3 has a potential for efficient biomass saccharification and ethanol production from lignocellulosic biomass.

Sequential high gravity ethanol fermentation and anaerobic digestion of steam explosion and organosolv pretreated corn stover

The present work investigates the suitability of pretreated corn stover (CS) to serve as feedstock for high gravity (HG) ethanol production at solids-content of 24wt%. Steam explosion, with and without the addition of H₂SO₄, and organosolv pretreated CS samples underwent a liquefaction/saccharification step followed by simultaneous saccharification and fermentation (SSF). Maximum ethanol concentration of ca. 76g/L (78.3% ethanol yield) was obtained from steam exploded CS (SECS) with 0.2% H₂SO₄. Organosolv pretreated CS (OCS) also resulted in high ethanol concentration of ca. 65g/L (62.3% ethanol yield). Moreover, methane production through anaerobic digestion (AD) was conducted from fermentation residues and resulted in maximum methane yields of ca. 120 and 69mL/g volatile solids (VS) for SECS and OCS samples, respectively. The results indicated that the implementation of a liquefaction/saccharification step before SSF employing a liquefaction reactor seemed to handle HG conditions adequately.

Production of high concentrated cellulosic ethanol by acetone/water oxidized pretreated beech wood

BACKGROUND

Lignocellulosic biomass is an abundant and inexpensive resource for biofuel production. Alongside its biotechnological conversion, pretreatment is essential to enable efficient enzymatic hydrolysis by making cellulose susceptible to cellulases. Wet oxidation of biomass, such as acetone/water oxidation, that employs hot acetone, water, and oxygen, has been found to be an attractive pretreatment method for removing lignin while producing less degradation products. The remaining enriched cellulose fraction has the potential to be utilized under high gravity enzymatic saccharification and fermentation processes for the cost-competing production of bioethanol.

RESULTS

Beech wood residual biomass was pretreated following an acetone/water oxidation process aiming at the production of high concentration of cellulosic ethanol. The effect of pressure, reaction time, temperature, and acetone-to-water ratio on the final composition of the pretreated samples was studied for the efficient utilization of the lignocellulosic feedstock. The optimal conditions were acetone/water ratio 1:1, 40 atm initial pressure of 40 vol% O₂ gas, and 64 atm at reaction temperature of 175 °C for 2 h incubation. The pretreated beech wood underwent an optimization step studying the effect of enzyme loading and solids content on the enzymatic liquefaction/saccharification prior to fermentation. In a custom designed free-fall mixer at 50 °C for either 6 or 12 h of prehydrolysis using an enzyme loading of 9 mg/g dry matter at 20 wt% initial solids content, high ethanol concentration of 75.9 g/L was obtained.

CONCLUSION

The optimization of the pretreatment process allowed the efficient utilization of beech wood residual biomass for the production of high concentrations of cellulosic ethanol, while obtaining lignin that can be upgraded towards high-added-value chemicals. The threshold of 4 wt% ethanol concentration that is required for the sustainable bioethanol production was surpassed almost twofold, underpinning the efficient conversion of biomass to ethanol and bio-based chemicals on behalf of the biorefinery concept.

Fermentative production of high titer citric acid from corn stover feedstock after dry dilute acid pretreatment and biodetoxification

The aim of this work is to study the citric acid fermentation by a robust strain Aspergillus niger SIIM M288 using corn stover feedstock after dry dilute sulfuric acid pretreatment and biodetoxification. Citric acid at 100.04g/L with the yield of 94.11% was obtained, which are comparable to the starch or sucrose based citric acid fermentation. No free wastewater was generated in the overall process from the pretreatment to citric acid fermentation. Abundant divalent metal ions as well as high titer of potassium, phosphate, and nitrogen were found in corn stover hydrolysate. Further addition of extra nutrients showed no impact on increasing citric acid formation except minimum nitrogen source was required. Various fermentation parameters were tested and only minimum regulation was required during the fermentation. This study provided a biorefining process for citric acid fermentation from lignocellulose feedstock with the maximum citric acid titer and yield.

Towards efficient bioethanol production from agricultural and forestry residues: Exploration of unique natural microorganisms in combination with advanced strain engineering

Production of fuel ethanol from lignocellulosic feedstocks such as agricultural and forestry residues is receiving increasing attention due to the unsustainable supply of fossil fuels. Three key challenges include high cellulase production cost, toxicity of the cellulosic hydrolysate to microbial strains, and poor ability of fermenting microorganisms to utilize certain fermentable sugars in the hydrolysate. In this article, studies on searching of natural microbial strains for production of unique cellulase for biorefinery of agricultural and forestry wastes, as well as development of strains for improved cellulase production were reviewed. In addition, progress in the construction of yeast strains with improved stress tolerance and the capability to fully utilize xylose and glucose in the cellulosic hydrolysate was also summarized. With the superior microbial strains for high titer cellulase production and efficient utilization of all fermentable sugars in the hydrolysate, economic biofuels production from agricultural residues and forestry wastes can be realized.

Deletion of JJJ1 improves acetic acid tolerance and bioethanol fermentation performance of Saccharomyces cerevisiae strains

OBJECTIVES

To improve tolerance to acetic acid that is present in lignocellulosic hydrolysates and affects bioethanol production by Saccharomyces cerevisiae.

RESULTS

Saccharomyces cerevisiae strains with improved tolerance to acetic acid were obtained through deletion of the JJJ1 gene. The lag phase of the JJJ1 deletion mutant BYΔJJJ1 was ~16 h shorter than that of the parent strain, BY4741, when the fermentation medium contained 4.5 g acetic acid/l. Additionally, the specific ethanol production rate of BYΔJJJ1 was increased (0.057 g/g h) compared to that of the parent strain (0.051 g/g h). Comparative transcription and physiological analyses revealed higher long chain fatty acid, trehalose, and catalase contents might be critical factors responsible for the acetic acid resistance of JJJ1 knockout strains.

CONCLUSIONS

JJJ1 deletion improves acetic acid tolerance and ethanol fermentation performance of S. cerevisiae.

Acceleration of biodetoxification on dilute acid pretreated lignocellulose feedstock by aeration and the consequent ethanol fermentation evaluation

BACKGROUND

Biodetoxification by the fungus Amorphotheca resinae ZN1 provides an effective way of inhibitor removal from pretreated lignocellulose feedstock and has been applied in the process of ethanol, biolipids, and lactic acid production. However, the long-time used and the consumption of considerable xylose in the pretreated materials reduced the process efficiency. The improvements of biodetoxification should be made to enhance the production of biochemical from lignocellulosic materials.

RESULTS

This study reported an acceleration method of A. resinae ZN1-based biodetoxification on the corn stover (CS) feedstock pretreated using dry dilute acid pretreatment. Under proper aeration and well-mixing condition, the conversion rate of furfural, 5-hydroxymethylfurfural (HMF), acetic acid, and typical phenolic compounds were significantly accelerated by more than twofolds faster, which resulted in the reduction of biodetoxification time from 96 h in the conventional process to 36 h. Simultaneous saccharification and ethanol fermentation assay on accelerated biodetoxification of the dry dilute acid pretreated CS feedstock achieved the similar ethanol titer (48.56 g/L of 36 h' accelerated biodetoxification vs. 50.00 g/L of 4 days' conventional biodetoxification) and yield (58.10 vs. 59.63 %). Substrate priority of inhibitors to sugars by A. resinae ZN1 was discovered and considerable xylose was reserved in the accelerated biodetoxification. Cell growth of A. resinae fungus in liquid medium and on pretreated CS solids revealed that the enhanced aeration enhanced the biodetoxification rate rather than the cell growth rate. Accelerated inhibitor conversion might come from the increased supply of cofactors of nicotinamide adenine dinucleotide or nicotinamide adenine dinucleotide phosphate from the step of aldehyde inhibitors to the corresponding acids, instead of cell mass increase.

CONCLUSION

Accelerated biodetoxification reduced the period of biodetoxification and retained the xylose components in the pretreated CS, which provided a practical method on improving process efficiency for cellulosic ethanol production from severe pretreated lignocellulose feedstock.

High titer L-lactic acid production from corn stover with minimum wastewater generation and techno-economic evaluation based on Aspen plus modeling

Technological potentials of l-lactic acid production from corn stover feedstock were investigated by experimental and techno-economic studies. An optimal performance with 104.5 g/L in l-lactic acid titer and 71.5% in overall yield from cellulose in corn stover to l-lactic acid using an engineered Pediococcus acidilactici strain were obtained by overcoming several technical barriers. A rigorous Aspen plus model for l-lactic acid production starting from dry dilute acid pretreated and biodetoxified corn stover was developed. The techno-economic analysis shows that the minimum l-lactic acid selling price (MLSP) was $0.523 per kg, which was close to that of the commercial l-lactic acid produced from starch feedstock, and 24% less expensive than that of ethanol from corn stover, even though the xylose utilization was not considered. The study provided a prototype of industrial application and an evaluation model for high titer l-lactic acid production from lignocellulose feedstock.

Simultaneous saccharification and co-fermentation of dry diluted acid pretreated corn stover at high dry matter loading: Overcoming the inhibitors by non-tolerant yeast

Dry dilute acid pretreatment (DDAP) is a promising method for lignocellulose bioconversion, although inhibitors generated during the pretreatment impede the fermentation severely. We developed the simultaneous saccharification and co-fermentation (SScF) of DDAP pretreated biomass at high solid loading using xylose fermenting Saccharomyces cerevisiae, SyBE005. Effect of temperature on SScF showed that ethanol yield at 34°C was 10.2% higher than that at 38°C. Ethanol concentration reached 29.5 g/L at 15% (w/w) dry matter loading, while SScF almost ceased at the beginning at 25% (w/w) dry matter loading of DDAP pretreated corn stover. According to the effect of the diluted hydrolysate on the fermentation of strain SyBE005, a fed-batch mode was developed for the SScF of DDAP pretreated corn stover with 25% dry matter loading without detoxification, and 40.0 g/L ethanol was achieved. In addition, high yeast inoculation improved xylose utilization and the final ethanol concentration reached 47.2 g/L.