Hydrolysis Of Wheat Straw Research Articles

Impact of particle size reduction on high gravity enzymatic hydrolysis of steam-exploded wheat straw

Economically feasible bioethanol production from lignocellulosic biomass requires solid loadings ≥ 15% dry matter (DM, w/w). However, increased solid loadings can lead to process difficulties, which are characterized by high apparent slurry viscosity, insufficient substrate mixing and limited water availability, resulting in reduced final glucose yields. To overcome these limitations, this study focused on enzymatic hydrolysis of 10–35% DM solid loadings with steam-exploded wheat straw in two different particle sizes. At solid loadings of 20 and 25% DM small particle size of ≤ 2.5 mm yielded 16.9 ± 1.1% and 10.2 ± 1.4% increased final glucose concentrations compared to large particle size of 30 ± 20 mm. Small particle size also positively influenced slurry viscosity and, therefore, miscibility. As a key finding of this investigation, high gravity enzymatic hydrolysis with solid loadings of 30–35% DM was indeed successfully employed when wheat straw was applied in small particle size. Here, the highest final glucose yield was achieved with 127.9 ± 4.9 g L−1 at 35% DM solid loading. An increase in the solid loading from 10 to 35% DM in small particle size experiments resulted in a 460% increase in the final glucose concentration.

Valorisation of wheat straw and bioethanol production by a novel xylanase- and cellulase-producing Streptomyces strain isolated from the wood-feeding termite, Microcerotermes species

Lignocellulosic biomass represents an unlimited and ubiquitous energy source, effectively addressing current global energy demand challenges. However, the recalcitrant nature of lignocellulose hinders microbial degradation, necessitating an appropriate hydrolytic enzyme production source for biomass valorisation and bioethanol production. This study might be the first to explore a novel bacterial species Streptomyces sp. strain MS-S2, isolated from the higher wood-feeding termite, Microcerotermes sp.; capable of concurrent degradation and saccharification of wheat straw for the liberation of reducing sugars, which can further be converted to bioethanol. The Streptomyces sp. MS-S2 demonstrated the capacity to efficiently utilise wheat straw as the sole carbon source for the secretion of xylanase and cellulase enzymes. The highest cellulase and xylanase productions were observed for ten days when the bacterium was cultured in the medium amended with 15 g/L of wheat straw and 1.5% yeast extract at pH 8.0, 30 ℃. Under optimum conditions, xylanase and cellulase activities were estimated to be 6.560 ± 0.160 and 0.866 ± 0.067 U/mL, respectively. Through Scanning electron microscopy analysis, the surface accessibility of cellulose fibrils in treated wheat straw was observed, indicating the efficiency of the hydrolysis process. In addition, functional group modifications from Fourier transform infrared spectroscopy analysis demonstrated the successful depolymerisation of wheat straw. Further, excreted enzymes produced under optimal conditions were applied to wheat straw hydrolysis for the liberation of reducing sugars. Then, ethanol production was obtained at a maximum concentration of 10.8 g/L. The findings of this study could open a new path for the search of new lignocellulolytic-producing bacteria inhabiting the gut symbionts of wood-feeding termites to valorise lignocellulosic biomass into biotechnologically value-added products such as biofuels.

Production of bioethanol from wheat straw via optimization of co-culture conditions of Bacillus licheniformis and Saccharomyces cerevisiae

Bioethanol production has been a challenge for the researchers with respect to enhancing the bioethanol yield. In this study, we are reporting an efficient novel method to produce bioethanol. The process comprises co-culture technique to produce bioethanol from wheat straw, by co-culturing Bacillus licheniformis and Saccharomyces cerevisiae. Simultaneous saccharification and fermentation allows wheat straw hydrolysis by cellulase enzyme produced by Bacillus licheniformis and conversion of produced reducing sugar into ethanol by Saccharomyces cerevisiae. Pre-treatment of wheat straw and optimization of co-culturing parameters like, time, pH, substrate concentrations and nitrogen source concentrations gave a net yield of ⁓ 4.11 g/l bioethanol. Scale up of optimised media to fermenter has resulted in a significant enhancement of bioethanol production to ⁓ 14.70 g/l.

Comparison of sulfomethylated lignin from poplar and masson pine on cellulase adsorption and the enzymatic hydrolysis of wheat straw

In this work, effects of sulfomethylated lignins (SLs) prepared from masson pine (SLM) and poplar (SLP) on enzymatic hydrolysis and cellulase-lignin interaction were comparatively investigated. The results showed that both SLM and SLP significantly promoted the substrate enzymatic digestibility. The total sugar yield increased from 38.6% to 74.4% and ∼ 100%, respectively at 10 FPU/g-cellulose of cellulase dosage. The protein content in hydrolysate linearly increased with the addition of SL (0 – 1.6 g/g-substrate lignin), which suggested the competitive adsorption of cellulase may occur to substrate lignin and SLs. Further structural analysis of lignin revealed the high S/(V + H) ratio was directly related to the high enzymatic saccharification efficiency. The strong interaction between SL and cellulase decreased the nonproductive adsorption of cellulase onto substrate lignin and increased the accessibility of cellulase to carbohydrate, which was considered to be the key factor for the improvement of substrate enzymatic digestibility.

Revealing the influence of metallic chlorides pretreatment on chemical structures of lignin and enzymatic hydrolysis of waste wheat straw

The addition of various metallic chlorides in pretreatment of lignocellulose have been widely reported to improve cellulose conversion via cellulolytic processing. However, the interaction mechanism between lignin and metallic cations is not well known. In this work, pretreatment with different concentrations of FeCl3 and AlCl3 were performed upon waste wheat straw to enhance enzymatic hydrolysis efficiency. Results showed that pretreatment with FeCl3 and AlCl3 could facilitate the enzymatic hydrolysis efficiency increasing from 50.4% to 82.9% and 76.6%, which was attributed to the enhancement of xylan removal by 33.8% (FeCl3) and 36.5% (AlCl3), respectively. Meanwhile, the surface charge, hydrophobicity, and protein adsorption capacity of lignin from waste wheat straw can be decreased by 3.3 mV, 0.6 L/g, 7.6 mg/g (FeCl3). This was due to the depolymerization of lignin in metallic chlorides pretreatment. These findings will be used to further evaluate the effect of metallic chlorides in biorefinery pretreatment.

Tolerance of Trichosporon cutaneum to lignin derived phenolic aldehydes facilitate the cell growth and cellulosic lipid accumulation

Phenolic aldehydes are the major inhibitors from lignocellulose pretreatment. Previous studies show that oleaginous yeasts are difficult to survive in lignocellulosic hydrolysates even after the removal of furan aldehydes and organic acids inhibitors. This study investigated the cell viability, sugar consumption and lipid accumulation of the major oleaginous yeasts including Trichosporon cutaneum, Rhodosporidium toruloides, Rhodotorula glutinis, Yarrowia lipolytica in wheat straw hydrolysate containing only phenolic aldehydes after furan aldehydes and organic acids were selectively degraded by microorganisms. The results confirmed that the existence of residual phenolic aldehydes was the major reason for poor cell growth and metabolism of oleaginous yeasts. Only T. cutaneum demonstrated the higher tolerance by biodegrading phenolic aldehydes and the satisfactory cell growth and lipid production were obtained. This study revealed that T. cutaneum might be one of the promising cell factories for microbial lipid production from lignocellulosic feedstock.

Maximizing the simultaneous production of lipids and carotenoids by Rhodosporidium toruloides from wheat straw hydrolysate and perspectives for large-scale implementation

This study aimed to select fermentation conditions able to simultaneously maximize the production of lipids and carotenoids by oleaginous yeast cultivated in wheat straw hydrolysate. An evolved strain of Rhodosporidium toruloides with improved tolerance to toxic compounds present in hydrolysate medium was used. Experiments were performed in order to investigate the effect of the temperature and inoculum load on the production of lipids and carotenoids by R. toruloides. Results revealed that the accumulation of both products can be simultaneously maximized when performing the fermentation at 17 °C and using 3.5 g/L of inoculum. This maximum simultaneous production opens up new perspectives for the establishment of a feasible and more sustainable large-scale process for the production of lipids and carotenoids. Even corresponding to only 1% of the cell mass, due to the high market value, carotenoids would account for more than 90% of the total income of the industrial plant.

Oleaginous yeasts respond differently to carbon sources present in lignocellulose hydrolysate

BackgroundMicrobial oils, generated from lignocellulosic material, have great potential as renewable and sustainable alternatives to fossil-based fuels and chemicals. By unravelling the diversity of lipid accumulation physiology in different oleaginous yeasts grown on the various carbon sources present in lignocellulose hydrolysate (LH), new targets for optimisation of lipid accumulation can be identified. Monitoring lipid formation over time is essential for understanding lipid accumulation physiology. This study investigated lipid accumulation in a variety of oleaginous ascomycetous and basidiomycetous strains grown in glucose and xylose and followed lipid formation kinetics of selected strains in wheat straw hydrolysate (WSH).ResultsTwenty-nine oleaginous yeast strains were tested for their ability to utilise glucose and xylose, the main sugars present in WSH. Evaluation of sugar consumption and lipid accumulation revealed marked differences in xylose utilisation capacity between the yeast strains, even between those belonging to the same species. Five different promising strains, belonging to the species Lipomyces starkeyi, Rhodotorula glutinis, Rhodotorula babjevae and Rhodotorula toruloides, were grown on undiluted wheat straw hydrolysate and lipid accumulation was followed over time, using Fourier transform-infrared (FTIR) spectroscopy. All five strains were able to grow on undiluted WSH and to accumulate lipids, but to different extents and with different productivities. R. babjevae DVBPG 8058 was the best-performing strain, accumulating 64.8% of cell dry weight (CDW) as lipids. It reached a culture density of 28 g/L CDW in batch cultivation, resulting in a lipid content of 18.1 g/L and yield of 0.24 g lipids per g carbon source. This strain formed lipids from the major carbon sources in hydrolysate, glucose, acetate and xylose. R. glutinis CBS 2367 also consumed these carbon sources, but when assimilating xylose it consumed intracellular lipids simultaneously. Rhodotorula strains contained a higher proportion of polyunsaturated fatty acids than the two tested Lipomyces starkeyi strains.ConclusionsThere is considerable metabolic diversity among oleaginous yeasts, even between closely related species and strains, especially when converting xylose to biomass and lipids. Monitoring the kinetics of lipid accumulation and identifying the molecular basis of this diversity are keys to selecting suitable strains for high lipid production from lignocellulose.

Scale-up of hydrogen and ethanol co-production by an engineered Escherichia coli

In this work, the scale-up from 0.01 to 10 L process for the co-production of hydrogen (H2) and ethanol (EtOH) by a genetically engineered Escherichia coli that utilizes hemicellulosic hydrolysates from wheat straw pretreated (WSP) as substrate is presented. Co-production of biofuels was performed through the redirection of carbon-flux to ethanol by deleting ldhA (D-lactate dehydrogenase) and frdD (fumarate reductase) genes in an H2-overproducer strain (E. coli WDH). Resulting strain, E. coli WDH-LF (ΔhycA ΔfrdD ΔldhA), increased up to 70% and 167% the H2 and EtOH production from glucose compared with the parenteral strain. Using WSP as substrate, the yields of H2 and EtOH remained constant at all the evaluated scales. In 10 L bioreactors, the production parameters such as maximum production, production rate and yield were 5,603.0 ± 233.5 mL H2/L, 41.4 ± 4.0 mL H2/L/h, 342.7 ± 14.3 mL H2/g TRS, 7.90 ± 0.28 g EtOH/L and 0.48 ± 0.01 g EtOH/g TRS, respectively. The results demonstrate the potential of the co-production of H2 and EtOH at different production scales by the engineered E. coli strain using lignocellulosic biomass as feedstock, such as wheat straw hydrolysates.

Enhanced ethanol production from lignocellulosic hydrolysates by Thermoanaerobacterium aotearoense SCUT27/ΔargR1864 with improved lignocellulose-derived inhibitors tolerance

The transcriptome data of Thermoanaerobacterium aotearoense SCUT27 (SCUT27) and Thermoanaerobacterium aotearoense SCUT27/ΔargR1864 (SCUT27/ΔargR1864) under xylose showed that ArgR1864 was the negative regulator for chaperonin synthesis. With argR1864 knockout, the mutant showed up-regulated expression of DnaK-DnaJ-GrpE system and GroEL-GroES chaperonin, which not only endowed the strain with the ability to scavenge the reactive oxygen species (ROS), but also gave the mutant the capability to maintain better cell growth, xylose consumption, acetic acid and ethanol production under the stress of various lignocellulose-derived inhibitors. Diluted acid pretreated soybean straw, sorghum stalk and wheat straw hydrolysates were used to evaluate the ethanol production of SCUT27/ΔargR1864 and results showed that the mutant definitely had advantages over SCUT27 for ethanol production under lignocellulosic hydrolysates, with the xylose consumption rate increased by 25.00%–44.83%, the ethanol production improved by 113.86%–366.36% and ethanol yield enhanced by 88.89%–208.33%.

Enzymatic hydrolysis of lignocellulosic biomass using native cellulase produced by Aspergillus niger ITV02 under liquid state fermentation.

The objective of this work was to evaluate the biochemical characteristics of an enzymatic extract obtained from autochthonous fungus Aspergillus niger ITV02 and its application in the enzymatic hydrolysis of wheat straw and corn stubble pretreated by steam explosion. The enzymatic extract was obtained by submerged fermentation using delignified sweet sorghum bagasse as a carbon source. The results obtained showed that the enzymatic extract had β-glucosidase and endoglucanase activities. The effects of pH and temperature on cellulase activity were evaluated and its thermostability was determined. The optimal parameters of the β-glucosidase and endoglucanase activities obtained were pH 5 and 70°C. The enzymatic extract of A. niger ITV02 was used to hydrolyze wheat straw and corn stubble, and the hydrolysis yields were compared with those obtained by a commercial cellulase (Celluclast 1.5L NS 50013) and CellicCTec3. The results showed that with the use the mixture of Celluclast 1.5L-A. niger ITV02 and CellicCTec3-A. niger ITV02 in the hydrolysis, conversions of 86.36% and 67.8% were obtained, respectively. Glucose production for the mixture extract increased 2.15 times more than when the enzyme was used independently alone. The present work shows that A. niger ITV02 has a potential as an enzyme producer for lignocellulosic hydrolysis.

Ethanol Production from Wheat Straw Hydrolysate by Issatchenkia Orientalis Isolated from Waste Cooking Oil

The interest in using non-conventional yeasts to produce value-added compounds from low cost substrates, such as lignocellulosic materials, has increased in recent years. Setting out to discover novel microbial strains that can be used in biorefineries, an Issatchenkia orientalis strain was isolated from waste cooking oil (WCO) and its capability to produce ethanol from wheat straw hydrolysate (WSHL) was analyzed. As with previously isolated I. orientalis strains, WCO-isolated I. orientalis KJ27-7 is thermotolerant. It grows well at elevated temperatures up to 42 °C. Furthermore, spot drop tests showed that it is tolerant to various chemical fermentation inhibitors that are derived from the pre-treatment of lignocellulosic materials. I. orientalis KJ27-7 is particularly tolerant to acetic acid (up to 75 mM) and tolerates 10 mM formic acid, 5 mM furfural and 10 mM hydroxymethylfurfural. Important for biotechnological cellulosic ethanol production, I. orientalis KJ27-7 grows well on plates containing up to 10% ethanol and media containing up to 90% WSHL. As observed in shake flask fermentations, the specific ethanol productivity correlates with WSHL concentrations. In 90% WSHL media, I. orientalis KJ27-7 produced 10.3 g L−1 ethanol within 24 h. This corresponds to a product yield of 0.50 g g−1 glucose (97% of the theoretical maximum) and a volumetric productivity of 0.43 g L−1 h−1. Therefore, I. orientalis KJ27-7 is an efficient producer of lignocellulosic ethanol from WSHL.

Comprehensive understanding of the effects of metallic cations on enzymatic hydrolysis of humic acid-pretreated waste wheat straw

BackgroundHumic acids (HA) have been used in biorefinery process due to its surfactant properties as an aid to the pretreatment of lignocellulose, with results indicating a positive effect on delignification. However, the HA remaining on the surface of the pretreated lignocellulose has also been shown to provide a negative effect on ensuing enzymatic digestibility. Hence, a strategy of complexing metallic cations with HA prior to enzymatic hydrolysis was proposed and demonstrated in this work in an effort to provide a means of HA mitigation that does not involve significant water consumption via extensive washing.ResultsResults showed that the enzymatic hydrolysis efficiency of waste wheat straw decreased from 81.9% to 66.1% when it was pretreated by 10 g/L HA, attributed to the inhibition ability of the residual HA on enzyme activity of cellulase with a debasement of 36.3%. Interestingly, enzymatic hydrolysis efficiency could be increased from 66.1% to 77.3% when 10 mM Fe3+ was introduced to the system and allowed to associate with HA during saccharification.ConclusionsThe addition of high-priced metallic cations (Fe3+) has successfully alleviated the effect of HA on cellulase activity. It is our hope in demonstrating the complexation affinity between metallic cations and HA, future researchers and biorefinery developers will evaluate this strategy as a unit operation that could allow economic biorefining of WWS to produce valuable biochemicals, biofuels, and biomaterials.

An integrated biorefinery process for co-production of xylose and glucose using maleic acid as efficient catalyst

This study aims to valorize wheat straw for xylose and glucose recovery using maleic acid in the pretreatment. The process conditions of maleic acid hydrolysis of wheat straw for xylose recovery were optimized by response surface methodology, through which the maximum xylose recovery of 77.12% versus minimum furfural yield of 1.61% were achieved using 70 g/L solid-to-liquid ratio and 0.1 mol/L maleic acid for 40 min at 150 °C. Moreover, 88.58% cellulose conversion was achieved by enzymatic hydrolysis of maleic acid-pretreated wheat straw. Results showed that maleic acid was an effective pretreatment solvent for sugars recovery: 19.88 g xylose and 30.89 g glucose were respectively obtained from 100 g wheat straw due to acidic and enzymatic hydrolysis, with only 0.37 g furfural produced. This study provides a strategy for hydrolyzing wheat straw to produce fermentable sugars with low amount of degradation product.

Optimization of steam explosion parameters for improved biotechnological use of wheat straw

Using lignocellulosic raw materials as substrate for biotechnological applications has been a focus of research during the last two decades. They contain sugars, which can be used in industrial fermentation processes, in from of polysaccharides (cellulose, hemicellulose). Wheat straw, one representative of lignocellulosic materials, is sustainably and abundantly available, especially in Europe and North America. However, wheat straw, just like any other lignocellulosic material, needs to be pretreated in one way or the other in order to generate sufficient quantities of monosaccharides. One widely used pretreatment for lignocellulosic material is steam explosion combined with enzymatic hydrolysis. In this study, the effects of steam exploding wheat straw in combination with water are presented. By impregnation with water, saccharide yields from subsequent enzymatic hydrolysis increased from 18.8 to 22.6 g L−1 for glucose and 13.8 to 16.4 g L−1 for xylose, respectively. Moreover, the basic steam explosion parameters residence time and temperature were optimized in ranges from 5 to 20 min and 180–200 °C. This further optimization increased the maximum saccharide yield to 41.2 g L−1 for glucose (200 °C, 15 min) and 18.9 g L−1 for xylose (190 °C, 10 min). Finally, the growth of the intensively investigated biotechnological production host Yarrowia lipolytica on hydrolysates derived from different steam explosion parameters was evaluated. Y. lipolytica grew well in media containing up to 90% wheat straw hydrolysate as sole carbon source, demonstrating the potential as substrate for biotechnological processes.

PRODUCTION OF XYLOSE REDUCTASE AND XYLITOL BY Candida guilliermondii USING WHEAT STRAW HYDROLYSATES

The objective of this study is to evaluate the production of Xylose reductase (XR) and Xylitol by Candida guilliermondii using wheat straw hydrolysates (WSH) supplemented with 2.0 g/l of (NH4)2SO4 and 0.1 g/l of CaCl2.2H2O as fermentation media . Wheat straw hydrolysis run at 121°C for 15 min. by diluted sulfuric acid . The fermentation process was conducted on a shaker bath (150 rpm) at 30C for 20 h in three separate flasks using different concentration of Xylose being , 30% Xylose , WSH(27.13 g/l Xylose)and WSH plus 30 g/l Xylose. The best concentration( WSH plus 30 g/l Xylose ) was chosen to run the fermentation process for XR production at different incubation temperature ( 20, 25, 30, 35, 40, 45 C, different pH values (5, 5.5, 6, 6.5 and 7) and different fermentation period (5 , 10 , 15,20 ,25 ,30 h ). The results indicated that the optimum condition for XR production was using 30%Xylose plus WSH at pH 6 over 20h incubation at 30 C. The crude extract of Xylose reductase was used to reduce Xylose into Xylitol with simultaneous oxidation of NADPH. The crude extract of XR was able to convert about 90 % 0f the Xylose to Xylitol through 24 h. incubation at 30°C.According to these findings WSH can be used as a promising source for Xylose to produce Xylose reductase enzyme by Candida guilliermondii and the crude extract could be used successfully in conversion of Xylose to Xylitol.

Evaluation of designed consortium SNH-1 for efficient hydrolysis of agriculture waste to benefit bioethanol production

Abstract An environment friendly and cost-effective approach is a major bottleneck in biofuels production from agriculture waste residue. The present study unravels the enzymatic hydrolytic potential of a designed bacterial consortium (SNH-1) comprised of camel rumen derived B. safensis CRN 13, B. subtilis CRN 16, C. braakii CRN 21, B. circulans CRN 24, and P. dendritiformis CRN18. The consortium SNH-1 was evaluated for exo-glucanase (0.29 U/ml), β-glucosidase (0.69U/ml), β-glucuronidase (0.29U/ml), endoxylanase (0.79U/ml), arabinosidase (0.62U/ml), α-galactosidase (0.36 U/ml), and endoglucanase (0.51U/ml) activity. Genome analysis of consortium members identified 660 carbohydrate-active enzymes (CAZyme) responsible for breaking the structural intricacy. These include 296 glycoside hydrolase, 19 auxiliary activity, 186 glycosyl transferases, and 37 carbohydrate-binding modules genes. The designed consortium hydrolyzed sugarcane bagasse, wheat straw, and rice straw effectively. Response surface methodology (RSM) was applied to optimize the pH, temperature, and substrate concentration, which has resulted in a 23% higher saccharification of wheat straw. Further, 6.2% bioethanol production was estimated from wheat straw hydrolysate using S. cerevisiae. The wheat straw saccharification by the designed consortium is a cost-effective, chemical-free, cleaner, and promising approach for producing lignocellulosic bioethanol.

Metabolic engineering of Aspergillus niger via ribonucleoprotein-based CRISPR\u2013Cas9 system for succinic acid production from renewable biomass

BackgroundSuccinic acid has great potential to be a new bio-based building block for deriving a number of value-added chemicals in industry. Bio-based succinic acid production from renewable biomass can provide a feasible approach to partially alleviate the dependence of global manufacturing on petroleum refinery. To improve the economics of biological processes, we attempted to explore possible solutions with a fungal cell platform. In this study, Aspergillus niger, a well-known industrial production organism for bio-based organic acids, was exploited for its potential for succinic acid production.ResultsWith a ribonucleoprotein (RNP)-based CRISPR–Cas9 system, consecutive genetic manipulations were realized in engineering of the citric acid-producing strain A. niger ATCC 1015. Two genes involved in production of two byproducts, gluconic acid and oxalic acid, were disrupted. In addition, an efficient C4-dicarboxylate transporter and a soluble NADH-dependent fumarate reductase were overexpressed. The resulting strain SAP-3 produced 17 g/L succinic acid while there was no succinic acid detected at a measurable level in the wild-type strain using a synthetic substrate. Furthermore, two cultivation parameters, temperature and pH, were investigated for their effects on succinic acid production. The highest amount of succinic acid was obtained at 35 °C after 3 days, and low culture pH had inhibitory effects on succinic acid production. Two types of renewable biomass were explored as substrates for succinic acid production. After 6 days, the SAP-3 strain was capable of producing 23 g/L and 9 g/L succinic acid from sugar beet molasses and wheat straw hydrolysate, respectively.ConclusionsIn this study, we have successfully applied the RNP-based CRISPR–Cas9 system in genetic engineering of A. niger and significantly improved the succinic acid production in the engineered strain. The studies on cultivation parameters revealed the impacts of pH and temperature on succinic acid production and the future challenges in strain development. The feasibility of using renewable biomass for succinic acid production by A. niger has been demonstrated with molasses and wheat straw hydrolysate.

Production of 2,3-Butanediol from non-detoxified wheat straw hydrolysate: Impact of microbial inhibitors on Paenibacillus polymyxa DSM 365

Lignocellulosic biomass (LB) is a cost-effective, readily available, and attractive substrate to produce 2,3-butanediol (2,3-BD) commercially. Fermentative conversion of non-detoxified wheat straw hydrolysate (WSH) to 2,3-BD was investigated using Paenibacillus polymyxa. The results show that P. polymyxa co-utilizes representative LB-derived sugars (glucose, xylose and arabinose). Comparatively, 2,3-BD fermentations with P. polymyxa in cultures containing glucose-xylose-arabinose in the ratio of 8:11:1 resulted in 1.03- and 1.18-fold increases in 2,3-BD yield and productivity, respectively, relative to glucose-only cultures (control). Subsequently, batch fermentations were conducted using 60 %, 80 %, and 100 % WSH and glucose-only control. P. polymyxa exhibited considerable tolerance to lignocellulose-derived microbial inhibitory compounds (LDMICs) in the 60 %, 80 % and 100 % WSH, as evidenced by growth, which increased 1.16-, 1.26- and 1.32-fold, respectively, when compared to the glucose-only control. The concentrations of 2,3-BD were 32, 31 and 23 g/L in 60 %, 80 % and 100 % WSH, respectively. These concentrations compare favorably to 32 g/L 2,3-BD produced with the glucose-only control without LDMICs. In addition, evaluation of the ability of P. polymyxa to transform LDMICs showed that P. polymyxa has the capacity to use HMF as a carbon source. These results underscore the potential of P. polymyxa for in situ detoxification and large-scale fermentation of WSH to 2,3-BD.

Candida intermedia CBS 141442: A Novel Glucose/Xylose Co-Fermenting Isolate for Lignocellulosic Bioethanol Production

The present study describes the isolation of the novel strain Candida intermedia CBS 141442 and investigates the potential of this microorganism for the conversion of lignocellulosic streams. Different C. intermedia clones were isolated during an adaptive laboratory evolution experiment under the selection pressure of lignocellulosic hydrolysate and in strong competition with industrial, xylose-fermenting Saccharomyces cerevisiae cells. Isolates showed different but stable colony and cell morphologies when growing in a solid agar medium (smooth, intermediate and complex morphology) and liquid medium (unicellular, aggregates and pseudohyphal morphology). Clones of the same morphology showed similar fermentation patterns, and the C. intermedia clone I5 (CBS 141442) was selected for further testing due to its superior capacity for xylose consumption (90% of the initial xylose concentration within 72 h) and the highest ethanol yields (0.25 ± 0.02 g ethanol/g sugars consumed). Compared to the well-known yeast Scheffersomyces stipitis, the selected strain showed slightly higher tolerance to the lignocellulosic-derived inhibitors when fermenting a wheat straw hydrolysate. Furthermore, its higher glucose consumption rates (compared to S. stipitis) and its capacity for glucose and xylose co-fermentation makes C. intermedia CBS 141442 an attractive microorganism for the conversion of lignocellulosic substrates, as demonstrated in simultaneous saccharification and fermentation processes.