Lignin isolated from steam-exploded eucalyptus wood chips by phase separation and its affinity to Trichoderma reesei cellulase

Naphthalene Structures Derived from Lignins During Phenolation

Phenolation is a commonly used method to improve the reactivity of lignin for various applications. In this study, resinol lignin models (syringaresinol and pinoresinol) and eucalyptus alkali lignin were treated under acid-catalyzed phenolation conditions to investigate the products derived from resinol (β-β) structures of lignins. The phenolation products were characterized by means of GC-MS and NMR spectroscopy following separation using flash chromatography and thin-layer chromatography. A series of new naphthalene products were identified from phenolation of syringaresinol, and the corresponding guaiacyl analogs were also identified by GC-MS. The C1-Cα bond of these resinol compounds was cleaved to release syringol or guaiacol during phenolation. In addition, diphenylmethane products formed from phenol or phenol and syringol/guaiacol were found in the phenolation products. Comparatively, more naphthalene products were obtained by phenolation from syringaresinol than those obtained from pinoresinol. HSQC NMR characterization of the phenolated alkali lignin revealed that naphthalene structures formed in the phenolated lignin.

The potential application of biosurfactant produced by Pseudomonas aeruginosa TGC01 using crude glycerol on the enzymatic hydrolysis of lignocellulosic material

The production of biosurfactant by Pseudomonas aeruginosa TGC01 using crude glycerol and sodium nitrate as the sole substrate and nitrogen source, respectively, was investigated using two mineral culture media. Two inoculum sizes (5 and 10% v/v) and two volumes of the culture medium (50 and 100 mL) in 500 mL Erlenmeyer flask also were used. Enzymatic hydrolyses of waste office paper (WOP), newspaper (NP) and eucalyptus wood chips (EWC) were carried out using the biosurfactant from P. aeruginosa TGC01. The decrease in volume of the culture medium increased the production of rhamnolipid by 500% in relation to concentration obtained when higher volume of culture medium was used. High quantity biosurfactant was recovered (11 g/L) with desired surface active properties after extraction using chloroform:methanol (v/v). The biosurfactant was able to reduce the water surface tension from 72 to 27 mN/m with a critical micelle concentration (CMC) of 100 mg/L and a stable emulsion index (above 60%) in the enzymatic hydrolysis (pH 4.8 and 50 °C for 4 h). Biosurfactant increased the glucose released in the enzymatic hydrolysis in relation to control (without tensoactive) when WOP (19% increase) and NP (113% increase) were used. The process for NP (18% lignin) was economical, given that the biosurfactant present made a delignification process unnecessary.

A structured understanding of cellobiohydrolase I binding to poplar lignin fractions after dilute acid pretreatment

BACKGROUND

Cellulase adsorption to lignin is considered a cost barrier for bioethanol production; however, its detailed association mechanism is still not fully understood. In this study, two natural poplar variants with high and low sugar release performance were selected as the low and high recalcitrant raw materials (named L and H, respectively). Three different lignin fractions were extracted using ethanol, followed by p-dioxane and then cellulase treatment from the dilute acid pretreated poplar solids (fraction 1, 2, and 3, respectively).

RESULTS

Each lignin fraction had different physicochemical properties. Ethanol-extracted lignin had the lowest weight average molecular weight, while the molecular weights for the other two lignin fractions were similar. ³¹P NMR analysis revealed that lignin fraction with higher molecular weight contained more aliphatic hydroxyl groups and less phenolic hydroxyl groups. Semi-quantitative analysis by 2D HSQC NMR indicated that the lignin fractions isolated from the natural variants had different contents of syringyl (S), guaiacyl (G) and interunit linkages. Lignin extracted by ethanol contained the largest amount of S units, the smallest amounts of G and p-hydroxybenzoate (PB) subunits, while the contents of these lignin subunits in the other two lignin fractions were similar. The lignin fraction obtained after cellulase treatment was primarily comprised of β-O-4 linkages with small amounts of β-5 and β-β linkages. The binding strength of these three lignin fractions obtained by Langmuir equations were in the order of L₁ > L₃ > L₂ for the low recalcitrance poplar and H₁ > H₂ > H₃ for the high recalcitrance poplar.

CONCLUSIONS

Overall, adsorption ability of lignin was correlated with the sugar release of poplar. Structural features of lignin were associated with its binding to CBH. For natural poplar variants, lignin fractions with lower molecular weight and polydispersity index (PDI) exhibited more CBH adsorption ability. Lignins with more phenolic hydroxyl groups had higher CBH binding strength. It was also found that lignin fractions with more condensed aromatics adsorbed more CBH likely attributed to stronger hydrophobic interactions.

Effective usage of sorghum bagasse: Optimization of organosolv pretreatment using 25% 1-butanol and subsequent nanofiltration membrane separation

We investigated the use of low concentrations of butanol (<40%, all v/v) as an organosolv pretreatment to fractionate lignocellulosic biomass into cellulose, hemicellulose, and lignin. The pretreatment conditions were optimized for sorghum bagasse by focusing on four parameters: butanol concentration, sulfuric acid concentration, pretreatment temperature, and pretreatment time. A butanol concentration of 25% or higher together with 0.5% or higher acid was effective for removing lignin while retaining most of the cellulose in the solid fraction. The highest cellulose (84.9%) and low lignin (15.3%) content were obtained after pretreatment at 200 °C for 60 min. Thus, pretreatment comprising 25% butanol, 0.5% acid, 200 °C, and 60 min process time was considered optimal. Enzymatic saccharification and fermentation by Saccharomyces cerevisiae produced 61.9 g/L ethanol from 200 g/L solid fraction obtained following pretreatment, and 10.2 g/L ethanol was obtained from the liquid fraction by xylose-utilizing S. cerevisiae following membrane nanofiltration to remove butanol.

Exoproteome analysis of Clostridium cellulovorans in natural soft-biomass degradation

Clostridium cellulovorans is an anaerobic, cellulolytic bacterium, capable of effectively degrading various types of soft biomass. Its excellent capacity for degradation results from optimization of the composition of the protein complex (cellulosome) and production of non-cellulosomal proteins according to the type of substrates. In this study, we performed a quantitative proteome analysis to determine changes in the extracellular proteins produced by C. cellulovorans for degradation of several types of natural soft biomass. C. cellulovorans was cultured in media containing bagasse, corn germ, rice straw (natural soft biomass), or cellobiose (control). Using an isobaric tag method and a liquid chromatograph equipped with a long monolithic silica capillary column/mass spectrometer, we identified 372 proteins in the culture supernatant. Of these, we focused on 77 saccharification-related proteins of both cellulosomal and non-cellulosomal origins. Statistical analysis showed that 18 of the proteins were specifically produced during degradation of types of natural soft biomass. Interestingly, the protein Clocel_3197 was found and commonly involved in the degradation of every natural soft biomass studied. This protein may perform functions, in addition to its known metabolic functions, that contribute to effective degradation of natural soft biomass.

Glycosylation of Cellulases: Engineering Better Enzymes for Biofuels

Cellulose in plant cell walls is the largest reservoir of renewable carbon on Earth. The saccharification of cellulose from plant biomass into soluble sugars can be achieved using fungal and bacterial cellulolytic enzymes, cellulases, and further converted into fuels and chemicals. Most fungal cellulases are both N- and O-glycosylated in their native form, yet the consequences of glycosylation on activity and structure are not fully understood. Studying protein glycosylation is challenging as glycans are extremely heterogeneous, stereochemically complex, and glycosylation is not under direct genetic control. Despite these limitations, many studies have begun to unveil the role of cellulase glycosylation, especially in the industrially relevant cellobiohydrolase from Trichoderma reesei, Cel7A. Glycosylation confers many beneficial properties to cellulases including enhanced activity, thermal and proteolytic stability, and structural stabilization. However, glycosylation must be controlled carefully as such positive effects can be dampened or reversed. Encouragingly, methods for the manipulation of glycan structures have been recently reported that employ genetic tuning of glycan-active enzymes expressed from homogeneous and heterologous fungal hosts. Taken together, these studies have enabled new strategies for the exploitation of protein glycosylation for the production of enhanced cellulases for biofuel production.

Increased enzymatic hydrolysis of sugarcane bagasse from enzyme recycling

BACKGROUND

Development of efficient methods for production of renewable fuels from lignocellulosic biomass is necessary to maximize yields and reduce operating costs. One of the main challenges to industrial application of the lignocellulosic conversion process is the high costs of cellulolytic enzymes. Recycling of enzymes may present a potential solution to alleviate this problem. In the present study enzymes associated with the insoluble fraction were recycled after enzymatic hydrolysis of pretreated sugarcane bagasse, utilizing different processing conditions, enzyme loadings, and solid loadings.

RESULTS

It was found that the enzyme blend from Chrysoporthe cubensis and Penicillium pinophilum was efficient for enzymatic hydrolysis and that a significant portion of enzyme activity could be recovered upon recycling of the insoluble fraction. Enzyme productivity values (g glucose/mg enzyme protein) over all recycle periods were 2.4 and 3.7 for application of 15 and 30 FPU/g of glucan, representing an increase in excess of ten times that obtained in a batch process with the same enzyme blend and an even greater increase compared to commercial cellulase enzymes.

CONCLUSIONS

Contrary to what may be expected, increasing lignin concentrations throughout the recycle period did not negatively influence hydrolysis efficiency, but conversion efficiencies continuously improved. Recycling of the entire insoluble solids fraction was sufficient for recycling of adhered enzymes together with biomass, indicative of an effective method to increase enzyme productivity.