Enzymatic Hydrolysis of Cellulose in Lignocellulosic Materials

Statistical media optimization and cellulase production from marine Bacillus VITRKHB

Marine Bacillus species are potent producers of novel enzymes. Marine Bacillus VITRKHB was observed to be efficient for cellulolytic activity. It was employed for the production of extracellular cellulase. Cellulase was partially purified to 1.6-fold in a stepwise manner by ammonium sulfate precipitation, dialysis, and DEAE ion exchange chromatography. The molecular weight of purified protein was found to be about 33 kDa by SDS-PAGE. Its specific activity was recorded as 1.92 IU/mg. The effect of various carbon and nitrogen sources on cellulase production was investigated. The maximum enzyme activity was recorded in the fermentation media containing xylose as carbon source and beef extract as nitrogen source. The combined interactive effect of different variables on cellulase production was studied by response surface methodology. The optimized combination of variables for maximum enzyme activity was determined as; xylose 5.0 %, beef extract 6.9 %, pH 7.83, NaCl 1.17, and temperature 25.84 °C, after 24 h of incubation.

Optimizing cellulase usage for improved mixing and rheological properties of acid-pretreated sugarcane bagasse

Consolidation of bioprocessing steps with lignocellulose is limited by hydrolysate toxicity, the fibrous nature of suspensions, and low activity of cellulase enzymes. Combinations of enzyme dose and treatment conditions improved the flow properties and pumping of acid-pretreated sugarcane bagasse slurries (10% dry weight). Low levels of cellulase enzyme (0.1 and 0.5 FPU/g dry weight acid-pretreated bagasse) were found to reduce viscosities by 77-95% after 6 h, solubilizing 3.5% of the bagasse dry weight. Flow of slurries through small funnels was a useful predictor of success with centrifugal and diaphragm pumps. Equations were derived that describe viscosity and solubilized carbohydrates as a function of time and cellulase dosage. Blending of acid-pretreated bagasse (10% dry weight) with suspensions of acid-pretreated bagasse (10% dry weight) that had been previously digested with cellulase enzymes (low viscosity) did not increase viscosity in a linear fashion. Viscosity of these mixtures remained relatively constant until a threshold level of new fiber was reached, followed by a rapid increase with further additions. Up to 35% fresh acid-pretreated bagasse could be blended with enzyme-digested fiber (5.0 FPU/g dry weight acid-pretreated fiber; 6 h) with only a modest increase in viscosity. The smooth surfaces of enzyme-treated fiber are proposed to hinder the frequency and extent of interactions between fibrils of fresh fiber particles (acid-pretreated) until a threshold concentration is achieved, after which fiber interactions and viscosity increase dramatically. These results were used to model the viscosity in an ideal continuous stirred tank reactor (liquefaction) as a function of residence time and enzyme dosage.

Identification of novel catalytic features of endo-beta-1,4-glucanase produced by mulberry longicorn beetle Apriona germari

Mulberry longicorn beetle, Apriona germari, has been reported to produce two endo-beta-1,4-glucanases or AgEGases (accession Nos. Q6SS52 and Q5XQD1). AgEGase sequence contains catalytic motif (amino acid residues 37-48), which is the characteristic of family Glycohydrolase 45 and is identified as the substrate binding site. The application of bioinformatics approaches includes sequence analysis, structural modeling and inhibitor docking to relate the structure and function of AgEGases. We have dissected the sequence and structure of AgEGase catalytic motif and compared it with crystal structure of Humicola insolens endoglucanases V. The results show an involvement of sulfur containing amino acid residues in the active site of the enzyme. Cys residues and position of disulfide bonds are highly conserved between the two structures of endoglucanases of A. germari. Surface calculation of AgEGase structure in the absence of Cys residues reveals greater accessibility of the catalytic site to the substrate involving Asp42, a highly conserved residue. For the inhibition study, tannin-based structure was docked into the catalytic site of AgEGase using ArgusLab 4.0 and it resulted in a stable complex formation. It is suggested that the inhibition could occur through formation of a stable transition state analog-enzyme complex with the tannin-based inhibitor, as observed with other insect cellulases in our laboratory.

The enzymes from extreme thermophiles: bacterial sources, thermostabilities and industrial relevance

This review on enzymes from extreme thermophiles (optimum growth temperature greater than 65 degrees C) concentrates on their characteristics, especially thermostabilities, and their commercial applicability. The enzymes are considered in general terms first, with comments on denaturation, stabilization and industrial processes. Discussion of the enzymes subsequently proceeds in order of their E.C. classification: oxidoreductases, transferases, hydrolases, lyases, isomerases and ligases. The ramifications of cloned enzymes from extreme thermophiles are also discussed.

Effects of an enzyme additive on composition of corn silage ensiled at various stages of maturity

Corn forage at the milk, soft dough, and black layer stages of maturity (22, 28, and 44% DM, respectively) was treated with an enzyme additive at 1, 10, or 100 times the recommended dose and ensiled in laboratory silos at 26 degrees C. By in vitro assay, the additive contained a full complement of cellulase and hemicellulase activities. The pH and temperature optima for cellulase and hemicellulase activities were 4.8 and 50 degrees C, respectively. Regardless of dose, the additive had no effect on fermentation acids or nitrogenous compounds in silage at any maturity; however, high doses increased the glucose content of silage at the milk stage of maturity and increased ethanol content at the soft dough stage. Across maturities, addition of the enzyme additive resulted in a linear decrease in ADF, NDF, and hemicellulose content of corn silage but decreased the acid detergent lignin content of silage only at the milk and black layer stages of maturity. The enzyme additive had no consistent effect on in vitro NDF digestion.

Cloning of endoglucanase genes from Cellulomonas biazotea into E. coli and S. cerevisiae using shuttle vector YEp24

We constructed a SmaI genomic library of Cellulomonas biazotea DNA in E. coli and in the S. cerevisiae shuttle vector, YEP 24. Three clone were identified that conferred the ability for E. coli or S. cerevisiae transformants to produce carboxymethylcellulase (CMCase). Cells transformed with these clones were compared with one another and with nontransformed cells for hyper-production of CMCase. In vivo and in vitro studies indicated that the CMCase genes were fully expressed and the enzyme activity was located extracellularly. The optimum pH and temperature for the CMCase thus cloned were pH 7 and 50 degrees C, respectively, as was the case for the donor.

The cellulose paradox: pollutant par excellence and/or a reclaimable natural resource?

The various aspects of cellulose as a pollutant are considered in view of its lack of toxicity on the one hand and its recalcitrant durable nature on the other. The microbial degradation of cellulosics is discussed, and the contrast between its success in handling natural cellulosic wastes versus its failure to cope with man-made refuse is described. Research carried out in the past decade has demonstrated that cellulolytic organisms are provided with cell surface multifunctional multienzyme conglomerates, called cellulosomes, which are capable of solubilizing solid cellulosic substrates. The intriguing properties of such complexes include their cohesive nature, their many enzymatic components, and a characteristic glycosylated cellulose-binding, 'scaffolding' component. The latter appears to serve as a substrate-targeting carrier, which delivers the other (hydrolytic) components to the cellulose. Progress in establishing efficient model systems for in vitro solubilization of purified cellulose or natural cellulosic substrates has been achieved using purified cellulosome preparations, fortified with beta-glucosidase and pectinase. The latter enzymes were required in order to alleviate the phenomenon of product inhibition which reduces the efficiency of the free cellulosome. Such combined enzyme systems are proposed as examples of future tailor-made cellulolytic systems for the degradation of natural cellulosics.

Digestion of cell wall components by dairy heifers fed diets based on alfalfa and chemically treated oat hulls

Four Holstein heifers were used in a 4 X 4 Latin square design to measure total tract digestion of cell wall components from diets based on alfalfa haylage and alkaline hydrogen peroxide-treated oat hulls. Diets contained 90% forage and 10% concentrate. Treatments were diets containing 90, 70, 50, or 30% alfalfa haylage with treated oat hulls supplying the remainder of the forage portion. Total tract digestion of cell wall-associated uronic acids, arabinose, galactose, mannose, rhamnose, and lignin were not affected by forage source. Digestibilities of cell wall glucose and xylose increased with increasing level of dietary treated oat hulls, reflecting the positive effect of alkaline hydrogen peroxide treatment on cell wall digestion. Cellulose (ADF minus acid detergent lignin) digestibilities were similar to those for cell wall glucose, whereas hemicellulose (NDF minus ADF) digestibilities were similar to those for cell wall arabinose plus xylose. Low digestibilities of alfalfa cell wall xylose indicate that some cell wall structure inhibits the degradation of alfalfa xylans. Low degradabilities of core lignin, esterified p-coumaric acid, and esterified acetyl groups suggest that these components may be involved primarily in depressing fermentation of cell wall polysaccharides.

Pleurotus mushrooms. Part III. Biotransformations of natural lignocellulosic wastes: commercial applications and implications

Species of Pleurotus are endowed with the capacity to degrade unfermented natural lignino-cellulosic wastes. From the time the substrate is spawned until the end of cropping, there occurs a spectrum of qualitative and quantitative changes in the various substrate constituents, viz., cellulose, hemicellulose, lignin, sugars, amino acids, phenols, ash, nitrogen, etc. In general, cellulose, hemicellulose, and lignin are degraded, solubility of the substrate is increased, phenolic content is decreased, sugar and amino acid contents are increased, as is the ash content due to a constant utilization of the organic matter. The ability of Pleurotus to effect these degradative changes is discussed under both sterile (monoculture) and nonsterile culturing conditions. The enzymatic aspects affecting these various chemical changes in the lignino-cellulosic substrates are brought out. The various commercial applications and implications of the spent substrate, such as use as an upgraded form of ruminant feed, production of biogas, manufacture of paper/cardboard, recycling into Agaricus compost, garden fertilizer, production of single cell proteins, etc., are critically evaluated.

Enzymatic degradation of cell wall and related plant polysaccharides

Polysaccharides such as starch, cellulose and other glucans, pectins, xylans, mannans, and fructans are present as major structural and storage materials in plants. These constituents may be degraded and modified by endogenous enzymes during plant growth and development. In plant pathogenesis by microorganisms, extracellular enzymes secreted by infected strains play a major role in plant tissue degradation and invasion of the host. Many of these polysaccharide-degrading enzymes are also produced by microorganisms widely used in industrial enzyme production. Most commerical enzyme preparations contain an array of secondary activities in addition to the one or two principal components which have standardized activities. In the processing of unpurified carbohydrate materials such as cereals, fruits, and tubers, these secondary enzyme activities offer major potential for improving process efficiency. Use of more defined combinations of industrial polysaccharases should allow final control of existing enzyme processes and should also lead to the development of novel enzymatic applications.