Mechanism of interaction between cellulase action and applied shear force, an hypothesis

Surface Modification of Decellularized Natural Cellulose Scaffolds with Organosilanes for Bone Tissue Regeneration

The utility of plant tissues as scaffolding materials has been gaining significant interest in recent years owing to their unique material characteristics that are ideal for tissue regeneration. In this study, the degradation and biocompatibility of natural cellulosic scaffolds derived from Borassus flabellifer (Linn.) (BF) immature endosperm was improved by chemical oxidation and surface functionalization processes. Briefly, thus obtained cellulosic scaffolds were sequentially processed via a detergent exchange decellularization process followed by sodium periodate mediated oxidation and organosilane-based surface modification using amino (NH₂)-terminated 3-aminopropyltriethoxysilane (APTES) and methyl (CH₃)-terminated octadecyltrichlorosilane (OTS). Post oxidation and surface functionalization, the scaffolds showed improved physiochemical, morphological, and mechanical properties. Especially, the swelling capacity, total porosity, surface area, degradation kinetics, and mechanical behavior of scaffold were significantly higher in modified scaffold groups. The biocompatibility analysis demonstrated excellent cellular adhesion, proliferation and differentiation of osteoblasts with an evident upregulation of mineralization. Subcutaneous implantation of these scaffolds in a rat model demonstrated active angiogenesis, enhanced degradation, and excellent biocompatibility with concomitant deposition of a collagen matrix. Taken together, the native cellulosic scaffolds post chemical oxidation and surface functionalization can exclusively integrate the potential properties of native soft tissue with ameliorated in vitro and in vivo support in bone tissue engineering for nonloading bearing applications.

Rice Straws With Different Cell Wall Components Differ on Abilities of Saccharification

Rice straw has an enormous amount of biomass for energy use, but the complexity of the cell wall component hinders technical processes. Although belonging to rice straws, the straws from different varieties should be with different treatment strategies to obtain best energy efficiency. To confirm this hypothesis, 7 different rice varieties (RPY GENG, RIL269, RIL272, RIL31, RIL57, RIL06, LUOHUI 9) with different cell wall traits from RIL population were evaluated for their response toward different pretreatments. For japonica RPY GENG, 2% of H₂SO₄ acid was best pre-treatment while high acid (5% of H₂SO₄) pretreatment caused undue loss. For Indica LUOHUI 9 rice, high acid pretreatment was suitable, while RIL57 had maximum of glucose yield with high alkali (10% NaOH) pretreatment. High-concentration alkali pretreatment is the most convenient and effective pretreatment method for the treatment of unknown varieties of rice straws, because the lignin has been removed and has the lowest negative effects on the glucose yield under the high alkali condition. As the RILs used in this study vary considerably in their wall structure, an understanding of their response to different pre-treatments confirms our hypothesis and help us to understand the influence of different wall compositions on the final output.

Profiling of Chemical and Structural Composition of Lignocellulosic Biomasses in Tetraploid Rice Straw

The improvement of the saccharification of rice straw is one of the strategies to reduce the sophisticated pretreatment that results in high cost and is unfriendly to the environment. We explored the cell wall features in tetraploid rice and highlighted the enhanced saccharification of tetraploid with large biomass. Results showed that lignin content and S/G ratio reduced to 17.09% and 0.37, respectively, in tetraploid straw by the determination of the pyGC-MS method. After the pretreatment, the cellulose crystallinity index decreased from 63.22% to 57.65% in tetraploid straw, which is lower than that of pretreated diploid straw. Surface topological analysis of SEM images indicated that tetraploid straw was more susceptible to the pretreatment. Tetraploid straw showed a strong advantage in the process of enzymatic hydrolysis. The enzyme efficiency reached the highest value of 77.60%, and the rate of enzyme reaction was improved to make the reaction saturated earlier than conventional rice. We concluded that the high saccharification has resulted from the alteration of lignin and cellulose in tetraploid rice. Our research provides an improved green feedstock for bioenergy, and the tetraploid rice straw shows the potential utilization value in bioethanol production.

Biofunctionalized Plants as Diverse Biomaterials for Human Cell Culture

The commercial success of tissue engineering products requires efficacy, cost effectiveness, and the possibility of scaleup. Advances in tissue engineering require increased sophistication in the design of biomaterials, often challenging the current manufacturing techniques. Interestingly, several of the properties that are desirable for biomaterial design are embodied in the structure and function of plants. This study demonstrates that decellularized plant tissues can be used as adaptable scaffolds for culture of human cells. With simple biofunctionalization technique, it is possible to enable adhesion of human cells on a diverse set of plant tissues. The elevated hydrophilicity and excellent water transport abilities of plant tissues allow cell expansion over prolonged periods of culture. Moreover, cells are able to conform to the microstructure of the plant frameworks, resulting in cell alignment and pattern registration. In conclusion, the current study shows that it is feasible to use plant tissues as an alternative feedstock of scaffolds for mammalian cells.

Cellulases: Classification, Methods of Determination and Industrial Applications

Microbial cellulases have been receiving worldwide attention, as they have enormous potential to process the most abundant cellulosic biomass on this planet and transform it into sustainable biofuels and other value added products. The synergistic action of endoglucanases, exoglucanases, and β-glucosidases is required for the depolymerization of cellulose to fermentable sugars for transformation in to useful products using suitable microorganisms. The lack of a better understanding of the mechanisms of individual cellulases and their synergistic actions is the major hurdles yet to be overcome for large-scale commercial applications of cellulases. We have reviewed various microbial cellulases with a focus on their classification with mechanistic aspects of cellulase hydrolytic action, insights into novel approaches for determining cellulase activity, and potential industrial applications of cellulases.

Enzymatic hydrolysis of steam-exploded sugarcane bagasse using high total solids and low enzyme loadings

Hydrolysis of phosphoric acid-impregnated steam-treated sugarcane bagasse was pre-optimized using a face-centered central composite design in which the process variables were the substrate total solids (TS, %), agitation intensity (AI, rpm) and enzyme loading (EL, gg(-1)). Pretreatment was carried out at 180°C for 10min using cane bagasse with 50wt% moisture content containing 9.5mg of H3PO4 per gram of dry biomass. Hydrolyses were performed for 96h at 50°C using Cellic CTec2® and water-washed steam-treated substrates. The highest amount of fermentable sugars was obtained with 20wt% TS, producing 76.8gL(-1) of glucose equivalents, which corresponded to a total glucan conversion of 69.2wt% and to a theoretical net increase of 39% in ethanol production from the same sugarcane tonnage without considering the use of leaves, tops and the additional yields from C5 sugars.

Addition of a carbohydrate-binding module enhances cellulase penetration into cellulose substrates

INTRODUCTION

Cellulases are of great interest for application in biomass degradation, yet the molecular details of the mode of action of glycoside hydrolases during degradation of insoluble cellulose remain elusive. To further improve these enzymes for application at industrial conditions, it is critical to gain a better understanding of not only the details of the degradation process, but also the function of accessory modules.

METHOD

We fused a carbohydrate-binding module (CBM) from family 2a to two thermophilic endoglucanases. We then applied neutron reflectometry to determine the mechanism of the resulting enhancements.

RESULTS

Catalytic activity of the chimeric enzymes was enhanced up to three fold on insoluble cellulose substrates as compared to wild type. Importantly, we demonstrate that the wild type enzymes affect primarily the surface properties of an amorphous cellulose film, while the chimeras containing a CBM alter the bulk properties of the amorphous film.

CONCLUSION

Our findings suggest that the CBM improves the efficiency of these cellulases by enabling digestion within the bulk of the film.

Enzymatic liquefaction and saccharification of pretreated corn stover at high-solids concentrations in a horizontal rotating bioreactor

A self-designed horizontal rotating bioreactor (HRR) was applied for enzymatic hydrolysis of pretreated corn stover to improve the process economics of ethanol production. The mixing principle was based on gravity and free fall employed with tank-rotating. The liquefaction performances using the HRR and the vertical stirred-tank reactor (VSTR) with a helical impeller were compared and analyzed by measuring rheological properties of the slurry. During the enzymatic hydrolysis, viscosity decreased dramatically in the initial phase for both bioreactors and more pronouncedly for the HRR. Rheological parameters fitted to the power law showed that shear thinning properties of the slurry weakened during the reaction. The glucose concentration was used to define the efficiency of the saccharification reaction. The HRR also proved to be more efficient for glucose release with both the constant and fed-batch substrate addition modes. Liquefaction and saccharification at 25% w/w dry matter (DM) and enzyme loading of 7 FPU/g DM resulted in the optimal glucose concentration of 86 g/kg. Results revealed a decrease in cellulose conversion at increasing initial DM, which was slighter in the HRR compared with that in the VSTR.

Torque measurements reveal large process differences between materials during high solid enzymatic hydrolysis of pretreated lignocellulose

BACKGROUND

A common trend in the research on 2nd generation bioethanol is the focus on intensifying the process and increasing the concentration of water insoluble solids (WIS) throughout the process. However, increasing the WIS content is not without problems. For example, the viscosity of pretreated lignocellulosic materials is known to increase drastically with increasing WIS content. Further, at elevated viscosities, problems arise related to poor mixing of the material, such as poor distribution of the enzymes and/or difficulties with temperature and pH control, which results in possible yield reduction. Achieving good mixing is unfortunately not without cost, since the power requirements needed to operate the impeller at high viscosities can be substantial. This highly important scale-up problem can easily be overlooked.

RESULTS

In this work, we monitor the impeller torque (and hence power input) in a stirred tank reactor throughout high solid enzymatic hydrolysis (< 20% WIS) of steam-pretreated Arundo donax and spruce. Two different process modes were evaluated, where either the impeller speed or the impeller power input was kept constant. Results from hydrolysis experiments at a fixed impeller speed of 10 rpm show that a very rapid decrease in impeller torque is experienced during hydrolysis of pretreated arundo (i.e. it loses its fiber network strength), whereas the fiber strength is retained for a longer time within the spruce material. This translates into a relatively low, rather WIS independent, energy input for arundo whereas the stirring power demand for spruce is substantially larger and quite WIS dependent. By operating the impeller at a constant power input (instead of a constant impeller speed) it is shown that power input greatly affects the glucose yield of pretreated spruce whereas the hydrolysis of arundo seems unaffected.

CONCLUSIONS

The results clearly highlight the large differences between the arundo and spruce materials, both in terms of needed energy input, and glucose yields. The impact of power input on glucose yield is furthermore shown to vary significantly between the materials, with spruce being very affected while arundo is not. These findings emphasize the need for substrate specific process solutions, where a short pre-hydrolysis (or viscosity reduction) might be favorable for arundo whereas fed-batch might be a better solution for spruce.

Preparation of Cross-Linked Cellulase Aggregates onto Magnetic Chitosan Microspheres

The cellulase was immobilized onto magnetic chitosan microspheres carrier as cross-linked enzymes aggregates (CLEAs). It was precipitated with 95% saturation ammonia sulfate and cross-linked with 3% (v/v) glutaraldehyde. Efficient enzyme activity about 50.6% was obtained when cellulase concentration was 1.0mg/mL after cross-linking for 7 h at 30○C. The CLEAs was advantageous on stabilities and magnetic responsiveness for separation.

Effect of mixing on enzymatic hydrolysis of steam-pretreated spruce: a quantitative analysis of conversion and power consumption

BACKGROUND

When scaling up lignocellulose-based ethanol production, the desire to increase the final ethanol titer after fermentation can introduce problems. A high concentration of water-insoluble solids (WIS) is needed in the enzymatic hydrolysis step, resulting in increased viscosity, which can cause mass and heat transfer problems because of poor mixing of the material. In the present study, the effects of mixing on the enzymatic hydrolysis of steam-pretreated spruce were investigated using a stirred tank reactor operated with different impeller speeds and enzyme loadings. In addition, the results were related to the power input needed to operate the impeller at different speeds, taking into account the changes in rheology throughout the process.

RESULTS

A marked difference in hydrolysis rate at different impeller speeds was found. For example, the conversion was twice as high after 48 hours at 500 rpm compared with 25 rpm. This difference remained throughout the 96 hours of hydrolysis. Substantial amounts of energy were required to achieve only minor increases in conversion during the later stages of the process.

CONCLUSIONS

Impeller speed strongly affected both the hydrolysis rate of the pretreated spruce and needed power input. Similar conversions could be obtained at different energy input by altering the mixing (that is, energy input), enzyme load and residence time, an important issue to consider when designing large-scale plants.

The effect of high intensity mixing on the enzymatic hydrolysis of concentrated cellulose fiber suspensions

Enzymatic hydrolysis of lignocellulosic biomass in a high shear environment was examined. The conversion of cellulose to glucose in samples mixed in a torque rheometer producing shear flows similar to those found in twin screw extruders was greater than that of unmixed samples. In addition, there is a synergistic effect of mixing and enzymatic hydrolysis; mixing increases the rate of cellulose conversion while the increased conversion facilitates mixing. The synergy appears to result in part from particle size reduction, which is more significant when hydrolysis occurs during intense mixing.

Nanoscale structure of the cell wall protecting cellulose from enzyme attack

The cell wall structure protects cellulose from enzymatic attack and its successive fermentation. The nature of this protection consists in the very complex macroscopic and microscopic structure of cell wall that limits transport. Explaining this kind of protection is critical in future research to improve cell polymer availability for enzymatic attack. This research shows that the complete description of the cell wall topography at a nanoscale level allows a mechanistic understanding of cellulose protection. For this purpose, we used gas adsorption methods (CO(2) at 273 K and N(2) at 77 K) to detect mesoporosity (pore size of 1.5-30 nm diameter; MeS) and microporosity (pore size of 0.3-1.5 nm diameter; MiS) of the cell wall of five energy crops, i.e., giant cane, rivet wheat straw, miscanthus, proso millet, and sorghum. The presence of both hemicelluloses in the spaces between cellulose fibrils and the unhydrolyzable and highly cross-linked lignocarbohydrate complex (LCC) determines a microporous (80% pores having diameters below 0.8 nm) structure of the cell wall that prevents the cellulase enzymes from coming into direct contact with the cellulose, as their sizes exceed the cell wall pore size. On the other hand, the removal of the hemicelluloses and of the LCC complex determines a reduction of the MiS and an increase of the available surface for enzymatic attack, i.e., pores >5 nm diameter. This was confirmed by the good negative (r = -0.87, P < 0.001, n = 11) and positive (r = 0.78, P < 0.005, n = 11) correlations found for microporosity and mesoporosity (pores of diameters >5 nm), respectively, vs the glucose production, by cellulase enzyme attack in specific enzymatic hydrolysis tests performed on biomass samples.

Purification and characterisation of alkaline cellulase produced by a novel isolate, Bacillus sphaericus JS1

A novel strain of Bacillus sphaericus JS1 producing thermostable alkaline carboxymethyl cellulase (CMCase; endo-1,4-beta-glucanase, E.C. 3.2.1.4) was isolated from soil using Horikoshi medium at pH 9.5. CMCase was purified 192-fold by (NH(4))(2)SO(4) precipitation, ion exchange and gel filtration chromatography, with an overall recovery of 23%. The CMCase is a multimeric protein with a molecular weight estimated by native-PAGE of 183 kDa. Using SDS-PAGE a single band is found at 42 kDa. This suggests presence of four homogeneous polypeptides, which would differentiate this enzyme from other known alkaline cellulases. The activity of the enzyme was significantly inhibited by bivalent cations (Fe(3+) and Hg(2+), 1.0 mM each) and activated by Co(2+), K(+) and Na(+). The purified enzyme revealed the products of carboxymethyl cellulose (CMC) hydrolysis to be CM glucose, cellobiose and cellotriose. Thermostability, pH stability, good hydrolytic capability, and stability in the presence of detergents, surfactants, chelators and commercial proteases make this enzyme potentially useful in laundry detergents.

Guidelines to come to minimized tensile strength loss upon cellulase application

Application of cellulase technology in the textile production process often results in a certain loss of tensile strength along with the desired performance. In this paper guidelines are given how to come to minimization or even prevention of tensile strength loss. Part of the considerations is based on the hypothesis given in the accompanying paper (Lenting and Warmoeskerken, 2001, J. Biotechnol.) concerning the mechanism of interaction between cellulase action and applied shear force. Recommendations given concern the enzyme choice, process parameters and enzyme targeting.