Hydrolysis Of Straw Research Articles

Effect of fungal pretreatment by Pycnoporus sanguineus and Trichoderma longibrachiatum on the anaerobic digestion of rice straw

Rice straw is composed of complex lignocellulosic biomass, representing a major obstacle in its conversion to bioenergy. The objective of this study was to evaluate the usefulness of less explored fungal strains Trichoderma longibrachiatum (TL) and Pycnoporus sanguineus (PS) in improving hydrolysis and bioavailability of rice straw in anaerobic digestion (AD). The fungal treatment of rice straw for 10 days by PS and TL increased biogas production by 20.79% and 17.85% and reduced soluble chemical oxygen demand (sCOD) by 71.43% and 64.70%, respectively. The AD samples containing fungal-treated rice straw showed higher lignocellulolytic enzyme activities contributing to better process performance. The taxonomic profile of microbial communities in treated samples showed increased diversity that could sustain consistent system performance and exhibit enhanced resilience against pH fluctuations. Metagenomic analysis revealed 60.82% increase in Proteobacteria in PS and 11.58% increase in Bacteroidetes in TL-treated rice straw samples resulting in improved hydrolysis.

Bioacetoin Production by Bacillus subtilis subsp. subtilis Using Enzymatic Hydrolysate of Lignocellulosic Biomass

Acetoin is an important bio-product useful in the chemical, food and pharmaceutical industries. Microbial fermentation is the major process for the production of bioacetoin, as the petroleum resources used in chemical methods are depleting day by day. Bioacetoin production using wild microorganisms is an easy, eco-friendly and economical method for the production of bioacetoin. In the present study, culture conditions and nutritional requirements were optimized for bioacetoin production by a wild and non-pathogenic strain of B. subtilis subsp. subtilis JJBS250. The bacterial culture produced maximum bioacetoin (259 mg L−1) using peptone (3%) and sucrose (2%) at 30 °C, 150 rpm and pH 7.0 after 24 h. Further supplementation of combinatorial nitrogen sources, i.e., peptone (1%) and urea (0.5%), resulted in enhanced titre of bioacetoin (1017 mg L−1) by the bacterial culture. An approximately 46.22–fold improvement in bioacetoin production was achieved after the optimization process. The analysis of samples using thin layer chromatography confirmed the presence of bioacetoin in the culture filtrate. The enzymatic hydrolysate was obtained by saccharification of pretreated rice straw and sugarcane bagasse using cellulase from Myceliophthora thermophila. Fermentation of the enzymatic hydrolysate (3%) of pretreated rice straw and sugarcane bagasse by the bacterial culture resulted in 210 and 473.17 mgL−1 bioacetoin, respectively. Enzymatic hydrolysates supplemented with peptone as a nitrogen source showed a two to four-fold improvement in the production of bioacetoin. Results have demonstrated the utility of wild type B. subtilis subsp. subtilis JJBS250 as a potential source for economical bioacetoin production by making use of renewable and cost-effective lignocellulosic substrate. Therefore, this study will help in the sustainable management of agricultural waste for the industrial production of bioacetoin, and in combating environmental pollution.

Minimization of Inhibitor Generation in Rice Straw Hydrolysate Using RSM Optimization Technique

Minimization of Inhibitor Generation in Rice Straw Hydrolysate Using RSM Optimization Technique

Adsorptive removal of inhibitors from paddy straw hydrolysate using surfactant-modified bentonite clay for fermentative xylitol production

Adsorptive removal of inhibitors from paddy straw hydrolysate using surfactant-modified bentonite clay for fermentative xylitol production

Metabolic engineering of Corynebacterium glutamicum for fatty alcohol production from glucose and wheat straw hydrolysate

BackgroundFatty acid-derived products such as fatty alcohols (FAL) find growing application in cosmetic products, lubricants, or biofuels. So far, FAL are primarily produced petrochemically or through chemical conversion of bio-based feedstock. Besides the well-known negative environmental impact of using fossil resources, utilization of bio-based first-generation feedstock such as palm oil is known to contribute to the loss of habitat and biodiversity. Thus, the microbial production of industrially relevant chemicals such as FAL from second-generation feedstock is desirable.ResultsTo engineer Corynebacterium glutamicum for FAL production, we deregulated fatty acid biosynthesis by deleting the transcriptional regulator gene fasR, overexpressing a fatty acyl-CoA reductase (FAR) gene of Marinobacter hydrocarbonoclasticus VT8 and attenuating the native thioesterase expression by exchange of the ATG to a weaker TTG start codon. C. glutamicum ∆fasR cg2692TTG (pEKEx2-maqu2220) produced in shaking flasks 0.54 ± 0.02 gFAL L−1 from 20 g glucose L−1 with a product yield of 0.054 ± 0.001 Cmol Cmol−1. To enable xylose utilization, we integrated xylA encoding the xylose isomerase from Xanthomonas campestris and xylB encoding the native xylulose kinase into the locus of actA. This approach enabled growth on xylose. However, adaptive laboratory evolution (ALE) was required to improve the growth rate threefold to 0.11 ± 0.00 h−1. The genome of the evolved strain C. glutamicum gX was re-sequenced, and the evolved genetic module was introduced into C. glutamicum ∆fasR cg2692TTG (pEKEx2-maqu2220) which allowed efficient growth and FAL production on wheat straw hydrolysate. FAL biosynthesis was further optimized by overexpression of the pntAB genes encoding the membrane-bound transhydrogenase of E. coli. The best-performing strain C. glutamicum ∆fasR cg2692TTG CgLP12::(Ptac-pntAB-TrrnB) gX (pEKEx2-maqu2220) produced 2.45 ± 0.09 gFAL L−1 with a product yield of 0.054 ± 0.005 Cmol Cmol−1 and a volumetric productivity of 0.109 ± 0.005 gFAL L−1 h−1 in a pulsed fed-batch cultivation using wheat straw hydrolysate.ConclusionThe combination of targeted metabolic engineering and ALE enabled efficient FAL production in C. glutamicum from wheat straw hydrolysate for the first time. Therefore, this study provides useful metabolic engineering principles to tailor this bacterium for other products from this second-generation feedstock.

Engineering Thermoanaerobacterium aotearoense SCUT27 with the deficiency of a hypothetic protein regulated by ArgR1864 for enhanced ethanol production from lignocellulosic hydrolysates

Arginine repressor (ArgR1864) is a multifunctional regulator in Thermoanaerobacterium aotearoense SCUT27 (SCUT27). For better understanding its function in SCUT27, the transcriptome of SCUT27/ΔargR1864 under xylose was further investigated. 2014 (V518_2014) denoted as a hypothetic protein gene was mined, which played important roles on xylose metabolism and carbon metabolic flux distribution in SCUT27. In 2014 deletion mutant, no lactic acid could be produced along with enhanced ethanol formation. Same changes were also observed in SCUT27/ΔargR1864. ArgR1864 is the direct regulator of 2014 identified by electrophoretic mobility shift assays (EMSA). When 2014 was complemented in SCUT27/ΔargR1864, the fermentation traits of SCUT27/ΔargR1864/2014 were returned to wild-type levels, suggesting that the improved xylose utilization and ethanol formation of SCUT27/ΔargR1864 were attributed to the low expression of 2014. When cultured under sorghum stalk, corn cob and wheat straw hydrolysates, SCUT27/Δ2014 also showed the excellent capability for sugar utilization and ethanol production with the consumption rate of xylose and glucose increased by 20%–37.93 and 64.29%–190.91% separately, the ethanol production improved by 326.61%–547.89% and ethanol yield enhanced by 216.67%–337.50%. Thus, 2014, as a hypothetic protein gene, could be used as the new genetic reference to predict functional genes to engineer the microorganism for biofuel production from lignocellulosic hydrolysates.

Influence of Tween 80 on enzymatic hydrolysis of corn straw integrated with membrane separation

This study aimed to investigate the influence of Tween 80 on the enzymatic hydrolysis of corn straw integrated with two-step membrane separation of reaction products and recovery of enzymes. Supplementation of the reaction mixture with 0.6% (w/v) Tween 80 resulted in an increased yield of hydrolysis carried out with Cellic® CTec2, both in batch and membrane bioreactor, compared to the enzymatic process conducted without surfactant. In the microfiltration membrane bioreactor, the glucan and xylan saccharification yields were, on average 31.2% and 25.5%, respectively, higher than without using Tween 80. Besides, the addition of Tween 80 significantly enhanced membrane permeability during hydrolysis without impacting its retention coefficients toward catalytic proteins. The ultrafiltration enables partial enzyme recovery and supply enzymes for a new hydrolysis process. Results obtained in this study proved the benefits of using Tween 80 in enzymatic hydrolysis of lignocellulosic biomass. Reduction of membrane fouling by surfactant during hydrolysis increases the filtration efficiency and extends the membrane lifetime.

Improved saccharification of rice straw by removing phenolic compounds using a stable immobilized metagenome-derived laccase on sodium alginate-based hydrogel

Laccases can biodegrade lignocellulosic agricultural waste, which has a recalcitrant structure hindering industrial biomass hydrolysis. In the context of biomass decomposition, introduction of a stabilized enzyme with enhanced performance is of critical importance. This study aimed to stabilize laccase, obtained from tannery metagenome (PersiLac2) on sodium alginate-based hydrogels. The immobilized laccase remained stable in the acidic and alkaline pH ranges and preserved over 79.39 % of its initial activity at pH 4.0–9.0. Similarly, immobilized enzyme improved laccase activity at high temperatures, which is crucial in biorefinery processes, and the immobilized enzyme demonstrated 88.35 % activity at 80 ºC. The immobilization of laccase on hydrogels effectively prevented enzyme leaching and rendered it easier to separate and recycle, showing 58.74 % laccase activity after 15 cycles. The efficiency of immobilized PersiLac2 in enzymatic hydrolysis of rice straw was evaluated to enhance the generation of fermentable sugars, saccharification, and phenol reduction. Laccase treatment of rice straw resulted in an excellent saccharification yield and liberation of reducing sugars and removed 77.19 % of phenols during hydrolysis. The depolymerization effect of free and immobilized laccase on rice straw was investigated by FTIR and SEM analyses which confirmed efficient structural disruption by immobilization. The results indicated the potential of immobilized Persilac2 to degrade the compact wrap of lignin–carbohydrate complex in lignocellulosic substrates and its application in biomass-based industries.

Development of yeast aerobic granules for long-term continuous bioethanol production from rice straw hydrolysate

For the first time application of aerobic granulation technology has been demonstrated for bioethanol production. A reactor was fabricated for ethanol production from rice straw hydrolysate (RSH) using Saccharomyces cerevisiae aerobic granules. The yeast granules were developed within 4–6 days by alternate aerobic mixing phase and settling phase without airflow of 8 h and 4 h, respectively. These yeast granules were found to produce ethanol (34.42 g/L) from pure glucose (80 g/L). A column filter was designed using activated charcoal, silica, cotton, and concrete aggregate to eliminate toxic impurities from RSH. Compared to unfiltered RSH, the filtered one was found to be more effective in ethanol production. A maximum of 16.18 g/L ethanol was produced from filtered RSH containing 10 g/L reducing sugar supplemented with pure glucose (40 g/L). It was possible to continuously run the process for more than 60 days. This study for the first time demonstrates continuous bioethanol production for an extended period by repeated use of yeast in the form of novel aerobic granules. This new concept has the potential to improve bioethanol production efficiencies of existing biorefineries.

Metabolic Engineering of Candida glycerinogenes for Sustainable Production of Geraniol.

Geraniol is a class of natural products that are widely used in the aroma industry due to their unique aroma. Here, to achieve the synthesis of geraniol and alleviate the intense competition from the yeast ergosterol pathway, a transcription factor-mediated ergosterol feedback system was developed in this study to autonomously regulate ergosterol metabolism and redirect carbon flux to geraniol synthesis. In addition, the modification of ergosterol-responsive promoters, the optimization of transcription factor expression intensity, and stepwise metabolic engineering resulted in a geraniol titer of 531.7 mg L-1. For sustainable production of geraniol, we constructed a xylose assimilation pathway in Candida glycerinogenes (C. glycerinogenes). Then, the xylose metabolic capacity was ameliorated and the growth of the engineered strain was rescued by activating the pentose phosphate (PP) pathway. Finally, we obtained 1091.6, 862.4, and 921.8 mg L-1 of geraniol in a 5 L bioreactor by using pure glucose, simulated wheat straw hydrolysates, and simulated sugarcane bagasse hydrolysates, with yields of 47.5, 57.9, and 59.1 mg g-1 DCW, respectively. Our study demonstrated that C. glycerinogenes has the potential to produce geraniol from lignocellulosic biomass, providing a powerful tool for the sustainable synthesis of other valuable monoterpenes.

Microbial fuel Cell-based Co-generation system for bioethanol production and power management solution

A Stacked Microbial Fuel Cell set-up using wheat straw hydrolysate as substrate is suitable for simultaneous ethanol production and power management solution. The system's performance is demonstrated by charging a standard 1.2 V and 3.7 V battery with three modules. The running time for ethanol production and the battery charging profiles of the microbial fuel cell is 300 min. It produces a maximum ethanol of 0.14 % (w/v) along with battery charging from 1.09 to 1.17 V, similarly, 0.12 % (w/v) of ethanol production along with battery charging from 3.50 to 3.57 V in 300 min. Additionally, a mathematical model estimates the possible production of ethanol and Open Circuit Voltage. Thus, the system may be further explored for possible industrial applications towards future energy sustainability by producing clean electricity and bioethanol on a large scale.

Characterization of a novel bifunctional enzyme from buffalo rumen metagenome and its effect on invitro ruminal fermentation and microbial community composition.

To efficiently use lignocellulosic materials in ruminants, it is crucial to explore effective enzymes, especially bifunctional enzymes. In this study, a novel stable bifunctional cellulase-xylanase protein from buffalo rumen metagenome was expressed and characterized, CelXyn2. The enzyme displayed optimal activity at pH 6.0 and 45°C. The residual endoglucanase and xylanase activities were 90.6% and 86.4% after a 60-min pre-incubation at 55°C. Hydrolysis of rice straw, wheat straw, sheepgrass and sugar beet pulp by CelXyn2 showed its ability to degrade both cellulose and hemicellulose polymers. Treatment with CelXyn2 improved the hydrolysis of agricultural residues with an evident increase in production of total gas, lactate and volatile fatty acids. The results of 16S rRNA and real-time PCR showed that the effect on invitro ruminal microbial community depended on fermentation substrates. This study demonstrated that CelXyn2 could strengthen lignocellulose hydrolysis and invitro ruminal fermentation. These characteristics of CelXyn2 distinguish it as a promising candidate for agricultural application.

Production of biohydrogen and green platform compound 2, 5-furandicarboxylic acid using rice straw hydrolysate

Lignocellulosic hydrolysate contains several inhibitors that hinder downstream biological processes. The immobilized strain Burkholderia sp. H-2 was used in this study to biodetoxify real rice straw hydrolysate and biotransform 5-hydroxymethylfurfural (5-HMF), an inhibitor, into 2, 5-furandicarboxylic acid (FDCA), a valuable platform compound. An electrodialysis with bipolar membranes (EDBM) system was applied to recover FDCA and perform secondary detoxification of the biodetoxified real rice straw hydrolysate. The rice straw hydrolysate after biodetoxification and EDBM treatment was used for anaerobic dark fermentative hydrogen production. The immobilized Burkholderia sp. H-2 could completely biotransform 1843 mg/L 5-HMF into 1532 mg/L FDCA within 24 h when the 2-fold diluted rice straw hydrolysate was used as the feedstock. The optimal EDBM system parameters to recover FDCA were a hydrolysate pH of 6, operated at a current density of 17.86 mA/cm2. The FDCA recovery efficiency was 44.6 %, when using the biodetoxified real rice straw hydrolysate as the EDBM feedstock. The rice straw hydrolysate after biodetoxification and EDBM treatment had better biohydrogen production performance than the undetoxified and biodetoxified rice straw hydrolysates.

Assessment of the TRX2p-yEGFP Biosensor to Monitor the Redox Response of an Industrial Xylose-Fermenting Saccharomyces cerevisiae Strain during Propagation and Fermentation.

The commercial production of bioethanol from lignocellulosic biomass such as wheat straw requires utilizing a microorganism that can withstand all the stressors encountered in the process while fermenting all the sugars in the biomass. Therefore, it is essential to develop tools for monitoring and controlling the cellular fitness during both cell propagation and sugar fermentation to ethanol. In the present study, on-line flow cytometry was adopted to assess the response of the biosensor TRX2p-yEGFP for redox imbalance in an industrial xylose-fermenting strain of Saccharomyces cerevisiae during cell propagation and the following fermentation of wheat-straw hydrolysate. Rapid and transient induction of the sensor was recorded upon exposure to furfural and wheat straw hydrolysate containing up to 3.8 g/L furfural. During the fermentation step, the induction rate of the sensor was also found to correlate to the initial ethanol production rate, highlighting the relevance of redox monitoring and the potential of the presented tool to assess the ethanol production rate in hydrolysates. Three different propagation strategies were also compared, and it was confirmed that pre-exposure to hydrolysate during propagation remains the most efficient method for high ethanol productivity in the following wheat-straw hydrolysate fermentations.

Enhancing enzymatic hydrolysis of waste sunflower straw by clean hydrothermal pretreatment

Hydrothermal pretreatment is an effective way to change the lignocellulose structure and improve its saccharification. An efficient hydrothermal pretreatment of sunflower straw was conducted when the severity factor (LogR0) was 4.1. 58.8% of xylan and 33.5% of lignin were removed at 180 °C for 120 min with a solid-to-liquid ratio of 1:15. A series of characterizations (such as X-ray diffraction, Fourier Transform infrared spectroscopy, scanning electron microscopy, chemical component analysis, cellulase accessibility) proved that hydrothermal pretreatment destroyed sunflower straw surface structure, enlarged its pores, and enhanced the accessibility to cellulase (371.2 mg/g). After the enzymatic saccharification of treated sunflower straw for 72 h, 68.0% yield of reducing sugar and 61.8% yield of glucose were achieved, and 3.2 g/L xylo-oligosaccharide was obtained in the filtrate. Overall, this easy-to-operate and green hydrothermal pretreatment could effectively destroy the surface barrier of lignocellulose, help remove lignin and xylan, and increase the enzymatic hydrolysis efficiency.

Cellulase mediated stress triggers the mutations of oleaginous yeast Trichosporon cutaneum with super-large spindle morphology and high lipid accumulation.

Accumulation of intracellular lipid bodies in oleaginous yeast cells is highly restricted by their natural intracellular space. Here we show a cellulase mediated adaptive evolution with ultra-centrifugation fractionation of oleaginous yeast Trichosporon cutaneum to obtain the favorable cell structure for lipid accumulation. Cellulase was added to the wheat straw hydrolysate during long-term adaptive evolution for disruption of cell wall integrity of T. cutaneum cells. The cellulase, together with ultracentrifugation force, triggered multiple mutations and transcriptional expression changes of the functional genes associated with cell wall integrity and lipid synthesis metabolism. The fractionated mutant T. cutaneum YY52 demonstrated the heavily weakened cell wall and high lipid accumulation by the super-large expanded spindle cells (two orders of magnitude greater than the parental). A record-high lipid production by T. cutaneum YY52 was achieved (55.4±0.5gL-1 from wheat straw and 58.4±0.1gL-1 from corn stover). This study not only obtained an oleaginous yeast strain with industrial application potential for lipid production but also provided a new method for generation of mutant cells with high intracellular metabolite accumulation.

Comparative study on the mild pretreatment processes for enzymatic hydrolysis of wheat straw with high-solid loading

Comparative study on the mild pretreatment processes for enzymatic hydrolysis of wheat straw with high-solid loading

Immobilization of cellulase on graphene oxide coated with NiFe2O4 and Fe3O4 for hydrolysis of rice straw

Immobilization of cellulase on graphene oxide coated with NiFe2O4 and Fe3O4 for hydrolysis of rice straw

Detoxification strategy of wheat straw hemicellulosic hydrolysate for cultivating Trichoderma reesei: a contribution towards the wheat straw biorefinery

The urgency for reducing the dependence on fossil-based materials is increasing the interest in the utilization of renewable feedstocks. Lignocellulosic residual biomass can be used as feedstock to produce chemicals and energy without generating food security problems. Wheat straw (WS) has a clear potential for developing sustainable processes in a circular bioeconomy context. However, the development of processes requires a strategy for utilizing the hemicellulosic, cellulosic, and lignin fractions. This work covers the utilization of the hemicellulosic fraction as the first stage of a wheat straw biorefinery. The aim was to evaluate the hydrolysis of WS by using liquid hot water (LHW) treatment, the detoxification of the produced wheat straw hydrolysate (WSH), and the cultivation of Trichoderma reesei using it as the only carbon source as proof of detoxification. LHW treatment was performed at 160 °C and 90 min and yielded a WSH rich in monomeric and oligomeric saccharides (~ 14 g/L) and containing degradation products in low concentration (furfural, HMF, and acetic acid). As part of the development of the extraction and detoxification strategy, we determined the specific inhibition thresholds for T. reesei for the mentioned degradation products. Detoxification was carried out by evaporation by modifying the % of volume evaporated and the pH of the solution. Approximately 55.9% of acetic acid and 100% of furfural were removed from the WSH. The fungal biomass obtained in the medium containing WSH was equivalent to 98% of the biomass obtained in the control medium.

Optimization of hydrolysis conditions of crop straw and its effect in Chlorellasorokiniana culture.

Taking straws of corn, wheat, and millet as raw materials, we pretreated them with alkaline hydrogen peroxide, and then hydrolyzed by cellulase and xylanase. We selected the total sugar content in the hydrolysate as the indicator to evaluate the hydrolysis of the straws from three crop species, and further optimized the conditions. Then, the hydrolysates of three types of crop straws were used as carbon source for Chlorella sorokiniana culture to assess their effects on microalgal cultivation. The results showed that the optimal hydrolysis conditions for the three crop straws were identified as solid-liquid ratio of 1:15, temperature of 30 ℃, and treatment time of 12 h. Under such optimal condition, the total sugar contents increased up to 1.677, 1.412, and 1.211 g·L-1 in the corn, millet and wheat straw hydrolysate, respectively. The hydrolysates from the three crop straw could significantly increase both algal biomass and lipid content of C. sorokiniana. Corn straw hydrolysate had the best effect, with high levels of algal biomass (1.801 g·L-1) and lipid content (30.1%). Therefore, we concluded that crop straw hydrolysates as carbon source could significantly promote microalgal biomass and lipid enrichment. The results could lay the foundation for the efficient conversion and utilization of straw lignocellulose raw materials, provide new knowledge for the resource utilization of agricultural wastes, as well as the theoretical basis for the efficient cultivation of microalgae using crop straw hydrolysates.