Screening of white-rot fungi for biological pretreatment of wheat straw for biogas production

Summary Twenty two basidiomycetes, mostly white rot fungi, were grown on wheat straw. Lignin-, cellulose-, and hemicellulose-degradation was recorded in order to find a species growing on lignin preferably. The oyster-mushroomPleurotus sp. florida showed fastest delignification of all tested fungi.Straw pretreated by this fungus was fermented anaerobically to biogas. The gas yield produced from myco-straw is twice the amount from untreated straw.     

Optimisation of a microwave pretreatment of wheat straw for methane production

This study aims at the optimisation of a microwave pretreatment for wheat straw solubilisation and anaerobic biodegradability. The maximum yield of methane production was obtained at 150 °C with an improvement of 28% compared to an untreated sample. In addition, at this temperature, the time to reach 80% of the methane volume obtained from untreated straw was about 35%. The study of ramp time and holding time at targeted temperature showed that they had no improvement effect. Thus, the best conditions are the highest heating rate for a final temperature 150 °C without any holding time. The reading of energy consumed by pretreatment and energy overproduced by pretreated samples showed that increasing tVS amount and heating rate led to a saving of energy consumption. Nevertheless, to obtain a positive energy balance, a microwave device should consume less than 2.65 kJ/g_tVS.     

The effectiveness of biological treatment of wheat straw by white-rot fungi

Out of 13 species ofBasidiomycetes growing on wheat straw, 9 species enhanced thein vitro dry matter digestibility of the substrate. The detergent fiber content (acid and neutral) of the substrate was significantly reduced by most of the fungi tested. Hemicellulose showed the largest proportionate loss, whereas lignin the smallest one.     

Modification of wheat straw lignin by solid state fermentation with white-rot fungi

The potential of crude enzyme extracts, obtained from solid state cultivation of four white-rot fungi (Trametes versicolor, Bjerkandera adusta, Ganoderma applanatum and Phlebia rufa), was exploited to modify wheat straw cell wall. At different fermentation times, manganese-dependent peroxidase (MnP), lignin peroxidase (LiP), laccase, carboxymethylcellulase (CMCase), avicelase, xylanase and feruloyl esterase activities were screened and the content of lignin as well as hydroxycinnamic acids in fermented straw were determined. All fungi secreted feruloyl esterase while LiP was only detected in crude extracts from B. adusta. Since no significant differences (P > 0.05) were observed in remaining lignin content of fermented straw, LiP activity was not a limiting factor of enzymatic lignin removal process. The levels of esterified hydroxycinnamic acids degradation were considerably higher than previous reports with lignocellulosic biomass. The data show that P. rufa, may be considered for more specific studies as higher ferulic and p-coumaric acids degradation was observed for earlier incubation times.     

Feasibility of filamentous fungi for biofuel production using hydrolysate from dilute sulfuric acid pretreatment of wheat straw

ABSTRACT: BACKGROUND: Lipids produced from filamentous fungi show great promise for biofuel production, but a major limiting factor is the high production cost attributed to feedstock. Lignocellulosic biomass is a suitable feedstock for biofuel production due to its abundance and low value. However, very limited study has been performed on lipid production by culturing oleaginous fungi with lignocellulosic materials. Thus, identification of filamentous fungal strains capable of utilizing lignocellulosic hydrolysates for lipid accumulation is critical to improve the process and reduce the production cost. RESULTS: The growth performances of eleven filamentous fungi were investigated when cultured on glucose and xylose. Their dry cell weights, lipid contents and fatty acid profiles were determined. Six fungal strains with high lipid contents were selected to culture with the hydrolysate from dilute sulfuric acid pretreatment of wheat straw. The results showed that all the selected fungal strains were able to grow on both detoxified liquid hydrolysate (DLH) and non-detoxified liquid hydrolysate (NDLH). The highest lipid content of 39.4% was obtained by Mortierella isabellina on NDLH. In addition, NDLH with some precipitate could help M. isabellina form pellets with an average diameter of 0.11 mm. CONCLUSION: This study demonstrated the possibility of fungal lipid production from lignocellulosic biomass. M. isabellina was the best lipid producer grown on lignocellulosic hydrolysates among the tested filamentous fungi, because it could not only accumulate oils with a high content by directly utilizing NDLH to simplify the fermentation process, but also form proper pellets to benefit the downstream harvesting. Considering the yield and cost, fungal lipids from lignocellulosic biomass are promising alternative sources for biodiesel production.     

Dilute acid pretreatment of rye straw and bermudagrass for ethanol production

Ethanol production from lignocellulosic materials provides an alternative energy production system. Rye and bermudagrass that are used in hog farms for nutrient uptake from swine wastewater have the potential for fuel ethanol production because they have a relative high cellulose and hemicellulose content. Dilute sulfuric acid pretreatment of rye straw and bermudagrass before enzymatic hydrolysis of cellulose was investigated in this study. The biomass at a solid loading rate of 10% was pretreated at 121 degrees C with different sulfuric acid concentrations (0.6, 0.9, 1.2 and 1.5%, w/w) and residence times (30, 60, and 90 min). Total reducing sugars, arabinose, galactose, glucose, and xylose in the prehydrolyzate were analyzed. In addition, the solid residues were hydrolyzed by cellulases to investigate the enzymatic digestibility. With the increasing acid concentration and residence time, the amount of arabinose and galactose in the filtrates increased. The glucose concentration in the prehydrolyzate of rye straw was not significantly influenced by the sulfuric acid concentration and residence time, but it increased in the prehydrolyzate of bermudagrass with the increase of pretreatment severity. The xylose concentration in the filtrates increased with the increase of sulfuric acid concentration and residence time. Most of the arabinan, galactan and xylan in the biomass were hydrolyzed during the acid pretreatment. Cellulose remaining in the pretreated feedstock was highly digestible by cellulases from Trichoderma reesei.     

Fungal pretreatment: An alternative in second-generation ethanol from wheat straw

The potential of a fungal pretreatment combined with a mild alkali treatment to replace or complement current physico-chemical methods for ethanol production from wheat straw has been investigated. Changes in substrate composition, secretion of ligninolytic enzymes, enzymatic hydrolysis efficiency and ethanol yield after 7, 14 and 21 days of solid-state fermentation were evaluated. Most fungi degraded lignin with variable selectivity degrees, although only eight of them improved sugar recovery compared to untreated samples. Glucose yield after 21 days of pretreatment with Poria subvermispora and Irpex lacteus reached 69% and 66% of cellulose available in the wheat straw, respectively, with an ethanol yield of 62% in both cases. Conversions from glucose to ethanol reached around 90%, showing that no inhibitors were generated during this pretreatment. No close correlations were found between ligninolytic enzymes production and sugar yields.     

Dilute acid pretreatment, enzymatic saccharification and fermentation of wheat straw to ethanol

Wheat straw consists of 48.57 ± 0.30% cellulose and 27.70 ± 0.12% hemicellulose on dry solid (DS) basis and has the potential to serve as a low cost feedstock for production of ethanol. Dilute acid pretreatment at varied temperature and enzymatic saccharification were evaluated for conversion of wheat straw cellulose and hemicellulose to monomeric sugars. The maximum yield of monomeric sugars from wheat straw (7.83%, w/v, DS) by dilute H₂SO₄ (0.75%, v/v) pretreatment and enzymatic saccharification (45 °C, pH 5.0, 72 h) using cellulase, β-glucosidase, xylanase and esterase was 565 ± 10 mg/g. Under this condition, no measurable quantities of furfural and hydroxymethyl furfural were produced. The yield of ethanol (per litre) from acid pretreated enzyme saccharified wheat straw (78.3 g) hydrolyzate by recombinant Escherichia coli strain FBR5 was 19 ± 1 g with a yield of 0.24 g/g DS. Detoxification of the acid and enzyme treated wheat straw hydrolyzate by overliming reduced the fermentation time from 118 to 39 h in the case of separate hydrolysis and fermentation (35 °C, pH 6.5), and increased the ethanol yield from 13 ± 2 to 17 ± 0 g/l and decreased the fermentation time from 136 to 112 h in the case of simultaneous saccharification and fermentation (35 °C, pH 6.0).     

Solid-state fermentation,lignin degradation and resulting digestibility of wheat straw fermented by selected white-rot fungi

Summary Lignin biodegradation, carbon loss and in vitro dry matter digestibility (IVDMD) have been investigated during the solid state fermentation of wheat straw by eight previously selected strains of white-rot fungi. A mathematical model of the degradation kinetics is presented. [The time period required to reach maximum rates of ¹⁴CO₂ and unlabeled CO₂ release from (¹⁴C)-lignin-labelled wheat straw and from whole wheat straw, respectively, was generally short (6–10 days).] High rates of ¹⁴C-lignin degradation were achieved by Pycnoporus cinnabarinus (2.9% ¹⁴CO₂ evolved/day), an unidentified strain Nancon (3.0%/day), Sporotrichum pulverulentum Nov. (3.4%/day), Bjerkandera adusta (2.4%/day), and Dichomitus squalens (2.3%). However, only the latter two strains degraded whole wheat straw slowly and Bjerkandera adusta was not able to degrade more than 23% of the ¹⁴C-lignin. Cyathus stercoreus and Dichomitus squalens facilitated the highest improvement in IVDMD (68% against 38% for the sound straw) after 20 and 15 days of cultivation respectively, with low dry matter losses (15–20%). A study of the fate of ¹⁴C-lignin during fermentation using these two fungal strains showed that maximal levels of (¹⁴C)-water-soluble compounds are reached before peak levels of ¹⁴CO₂ evolution suggesting that these compounds are intermediates in lignin degradation. A possible relationship between water-soluble lignins and IVDMD improvement is discussed.     

Effect of inhibitors formed during wheat straw pretreatment on ethanol fermentation by Pichia stipitis

The inhibitory effect of the main inhibitors (acetic acid, furfural and 5-hydroxymethylfurfural) formed during steam explosion of wheat straw was studied through ethanol fermentations of model substrates and hydrolysates from wheat straw by Pichia stipitis. Experimental results showed that an increase in acetic acid concentration led to a reduction in ethanol productivity and complete inhibition was observed at 3.5 g/L. Furfural produced a delay on sugar consumption rates with increasing concentration and HMF did not exert a significant effect. Fermentations of the whole slurry from steam exploded wheat straw were completely inhibited by a synergistic effect due to the presence of 1.5 g/L acetic acid, 0.15 g/L furfural and 0.05 g/L HMF together with solid fraction. When using only the solid fraction from steam explosion, hydrolysates presented 0.5 g/L of acetic acid, whose fermentations have submitted promising results, providing an ethanol yield of 0.45 g ethanol/g sugars and the final ethanol concentration reached was 12.2 g/L (10.9 g ethanol/100 g DM).     

Biogas production from the brown seaweed Saccharina latissima: thermal pretreatment and codigestion with wheat straw

Saccharina latissima is a carbohydrate-rich fast-growing seaweed (SW) which may be utilized as a marine energy crop. In this study, S. latissima was anaerobically digested for biogas production, and the effects of thermal pretreatment and codigestion with wheat straw (WS) were investigated. Batch experiments showed that pretreatment of SW increased the methane yield from 223 to 268 mL g^-1 VS. Codigestion of SW and steam-exploded WS had a clear positive effect on biogas production, giving yields that were considerably higher than what would be expected on the basis of the yields obtained with either of the individual feedstocks. Thus, anaerobic digestion of blends of SW and lignocellulosic substrates provides a promising strategy for biogas production. Although thermal pretreatment increased the yield of biogas from SW such a harsh pretreatment is probably more relevant for the more recalcitrant lignocellulosic substrates.     

Identification of white-rot and soft-rot fungi increasing ethanol production from spent sulfite liquor in co-culture with Saccharomyces cerevisiae

Aim:  To identify fungi that are capable of increasing ethanol production from lignocellulose in spent sulfite liquor.
Methods and Results:  In a batch fermentation study, the fungal mix could produce 24·61 g l⁻¹ ethanol using spent sulfite liquor as substrate. The fungal mix grew well on glucose, xylose, hemicellulose and cellulose. In addition, we were able to identify the fungal mix by use of PCR-amplification of DNA and sequencing, and they were identified as Chalara parvispora and Trametes hirsuta/T. versicolor. In a reconstitution study, the identified fungi were shown to produce equal amount of ethanol as the fungal mix. We were also able to show that C. parvispora could produce ethanol from xylose.
Conclusion:  The present study has shown that ethanol production from biomass can be increased by use of C. parvispora and T. versicolor when compared with fermentation using only S. cerevisiae .
Significance and Impact of the Study:  The study shows that refining biomass by ethanol production from spent sulfite liquor, a lignocellulose material, can be increased by adding C. parvispora and T. versicolor , and it is thus of great potential economical impact.     

Screening of white-rot fungi on (14C)lignin-labelled and (14C)whole-labelled wheat straw

Summary 74 Basidiomycetes have been tested for ligninolytic capability on (¹⁴C)lignin-labelled wheat straw. Fifteen strains were selected and rested more accurately for ligninolytic activity and the capacity to degrade wheat straw. The asymptote, inflexion point and degradation rate were determined using a model approach. The fungi exhibited very different responses with respect to lignin biodegradation: high asymptote for Pleurotus ostreatus (77%), low inflexion points for Sporotrichum pulverulentum Nov. (6.1 days) and Pycnoporus spp. (2.7 to 4.7 days) with high and slow degradation rates, respectively (0.91% and 0.45% of ¹⁴CO₂ release/day). Degradation values for (¹⁴C)whole-labelled wheat straw exhibited less variation. Finally, the strains Pleurotus ostreatus, Dichomitus squalens and Bjerkandera adusta showed the highest selectivity of lignin removal.     

Oil production by oleaginous yeasts using the hydrolysate from pretreatment of wheat straw with dilute sulfuric acid

This paper explores the use of the hydrolysate from the dilute sulfuric acid pretreatment of wheat straw for microbial oil production. The resulting hydrolysate was composed of pentoses (24.3 g/L) and hexoses (4.9 g/L), along with some other degradation products, such as acetic acid, furfural, and hydroxymethylfurfural (HMF). Five oleaginous yeast strains, Cryptococcus curvatus, Rhodotorula glutinis, Rhodosporidium toruloides, Lipomyces starkeyi, and Yarrowia lipolytica, were evaluated by using this hydrolysate as substrates. The results showed that all of these strains could use the detoxified hydrolysate to produce lipids while except R. toruloides non-detoxified hydrolysate could also be used for the growth of all of the selective yeast strains. C. curvatus showed the highest lipid concentrations in medium on both the detoxified (4.2 g/L) and non-detoxified (5.8 g/L) hydrolysates. And the inhibitory effect studies on C. curvatus indicated HMF had insignificant impacts at a concentration of up to 3 g/L while furfural inhibited cell growth and lipid content by 72.0% and 62.0% at 1 g/L, respectively. Our work demonstrates that lipid production is a promising alternative to utilize hemicellulosic sugars obtained during pretreatment of lignocellulosic materials.     

Paddy straw as substrate for ethanol production

Pretreatment of paddy straw with 2% sodium hydroxide at 15 psi for 1 h resulted in 83% delignification. The hydrolysis of alkali treated paddy straw with a commercial preparation of cellulase for 2 h at 50°C resulted in release of 65% total reducing sugars. Maximum sugars were released at enzyme loading of 1.5% (v/v). The fermentation of hydrolysate supplemented with nutrients by S. cerevisiae resulted in the production of 20–30 g L⁻¹ ethanol after 48 h incubation which was further improved with addition of yeast nitrogen base and inoculated with 1% (w/v) yeast cells.     

The pretreatment effect on wheat straw saccharification

Enzymatic hydrolysis of cellulose is potentially an attractive method for converting cellulose into glucose which can then be used as a chemical feed or as a growth substrate for a number of microorganisms to produce microbial products. An enzymatic hydrolysis of wheat straw with cellulase preparation “Trichocease” was made. The wheat straw used was pretreated mechanically and with NaOH. A procedure of pretreatment was investigated in 26 variants. The dynamics of enzymatic hydrolysis was studied. An assay of this dynamics based on the amount of reducing sugars formed during the cellulase reaction and depending upon enzyme and substrate concentration and time of action was carried out.     

乙醇预处理麦秆的酶解性能研究简

采用H2 SO4催化和自催化乙醇法对麦秆进行预处理,比较预处理后麦秆的主要化学组成、纤维素酶解性能和半同步糖化发酵生产乙醇特性,并进行物料衡算。结果表明：H2 SO4催化和自催化乙醇预处理过程中纤维素固体回收率大于90％。添加非离子表面活性剂吐温20和吐温80没有显著提高H2 SO4催化乙醇预处理后纤维素的酶解葡萄糖得率及半同步糖化发酵过程中乙醇的产量,而对自催化乙醇处理后麦秆的酶解和半同步糖化发酵过程有一定程度的促进作用,相应的酶解葡聚糖转化率由72.7％提高到85.0％,而半同步糖化发酵过程中乙醇质量浓度提高了11.4％。物料衡算结果表明：酸催化和自催化乙醇预处理后葡聚糖回收率分别为91.0％和95.4％;半同步糖化发酵生产乙醇的得率分别为10.4和11.6 g（按100 g原料计）。     

Optimization of organic acid pretreatment of wheat straw

The objective of this study was to determine the effectiveness of different organic acids (maleic, succinic, and oxalic acid) on enzymatic hydrolysis and fermentation yields of wheat straw. It was also aimed to optimize the process conditions (temperature, acid concentration, and pretreatment time) by using response surface methodology (RSM). In line with this objective, the wheat straw samples were pretreated at three different temperatures (170, 190, and 210°C), acid concentrations (1%, 3%, and 5%) and pretreatment time (10, 20, and 30 min). The findings show that at extreme pretreatment conditions, xylose was solubilized in liquid phase, causing an increase in cellulose and lignin content of biomass. Enzymatic hydrolysis experiments revealed that maleic and oxalic acids were quite effective at achieving high sugar yields (>90%) from wheat straw. In contrast, the highest sugar yields were 50–60%, when the samples were pretreated with succinic acid, indicating that succinic acid was not as effective. The optimum process conditions for maleic acid were, 210°C, 1.08% acid concentration, and 19.8 min; for succinic acid 210°C, 5% acid concentration, and 30 min; for oxalic acid 210°C, 3.6% acid concentration, and 16.3 min. The ethanol yields obtained at optimum conditions were 80, 79, and 59% for maleic, oxalic and succinic acid, respectively. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:1487–1493, 2016     

白腐真菌Pleurotus sajor-caju预处理对红麻秸秆发酵乙醇的影响

为研究微生物法预处理对红麻秸秆中木质素的降解及后续的红麻纤维素酶促糖化和发酵效率的影响,将白腐真菌Pleurotus sajor-caju接种在红麻秸秆培养基上固态培养,对红麻秸秆进行预处理。经P. sajor-caju培养25~35 d后,有效转化红麻秸秆中的木质素,转化率最高可达50.20％,并提高红麻纤维素的酶促水解效率,糖化率达69.33％~78.64％,与对照组相比提高了3.5~4.1倍。以微生物法预处理后的红麻秸秆样品为底物的同步糖化发酵实验表明,发酵72 h,发酵液中乙醇浓度达到18.35~