Enzymology of cellulose degradation

Effect of Enzymatic Biotransformation on the Hypotensive Potential of Red Grape Pomace Extract

Hypertension is a widespread health risk, affecting over a billion people and causing 9 million deaths per year. The Renin-Angiotensin-Aldosterone System (RAAS) is a primary target for hypertension treatment, and it is primarily treated through drugs that inhibit the Angiotensin I-Converting Enzyme (ACE). In addition to pharmacological treatment, various plants are recommended in traditional medicine for blood pressure regulation. This study aimed to produce high-phenolic-content extracts with and without enzymatic assistance from red grape pomace and evaluate their antioxidant capacity and ACE inhibitory potential. The total phenolic content (TPC) was measured, and phenolic identification was performed using HPLC analysis. In addition, the antioxidant capacity and anti-hypertensive potential were determined via in vitro assays. There was no statistical difference in the TPC antioxidant capacity between the extraction methods. Otherwise, when considering the extraction yield, the enzymatic process recovered around 70% more phenolic compounds from the pomace, and the phenolic profile was changed. Enzymatic assistance also significantly increased the ACE inhibitory potential in the grape pomace extract. This study demonstrates the viability of upcycling grape pomace to obtain bioactive compounds and to reduce their environmental impact, and highlights the influence of the enzymatic extraction on the hypotensive potential of the extract.

β-Glucosidase activity and antimicrobial properties of potentially probiotic autochthonous lactic cultures

Background

The demand for lactic acid bacteria products, especially probiotics, has increased. Bacteria that increase polyphenol bioavailability and act as bio preservatives are sought after. This study aims to identify autochthonous lactic acid cultures from EMBRAPA that demonstrate β-glucosidase activity and inhibitory effect on microbial sanitary indicators.

Methods

Cell-free extracts were obtained by sonicating every 5 s for 40 min. The extracts were mixed with cellobiose and incubated at 50 °C. The reaction was stopped by immersing the tubes in boiling water. The GOD-POD reagent was added for spectrophotometer readings. Antimicrobial activity was tested against reference strains using the agar well diffusion method. Lactic cultures in MRS broth were added to 0.9 cm wells and incubated. The diameter of the inhibition zones was measured to determine the extension of inhibition.

Results

Only L. rhamnosus EM1107 displayed extracellular β-glucosidase activity, while all autochthonous strains except L. plantarum CNPC020 demonstrated intracellular activity for this enzyme. L. plantarum CNPC003 had the highest values. On the other hand, L. plantarum CNPC020, similarly to L. mucosae CNPC007, exhibited notable inhibition against sanitary indicators. These two strains significantly differed from the other five autochthonous cultures regarding S. enterica serovar Typhimurium ATCC 14028 inhibition (P < 0.05). However, they did not differ from at least one positive control in terms of inhibition against S. aureus ATCC 25923 and E. coli ATCC 25922 (P > 0.05). Therefore, it is advisable to consider these cultures separately for different technological purposes, such as phenolics metabolism or bio preservative activity. This will facilitate appropriate selection based on each specific property required for the intended product development.

Profiling of the β-glucosidases identified in the genome of Penicillium funiculosum: insights from genomics, transcriptomics, proteomics, and homology-modeling studies

The enzymatic conversion of lignocellulosic biomass to bioethanol depends on efficient enzyme systems with β-glucosidase as one of the key components. In this study, we performed in-depth profiling of the various β-glucosidases present in the genome of the hypercellulolytic fungus Penicillium funiculosum using genomics, transcriptomics, proteomics, and molecular dynamics simulation approaches. Of the eight β-glucosidase genes identified in the P. funiculosum genome, three were predicted to be extracellular based on signal peptide prediction and abundance in the secretome. Among the three secreted β-glucosidases, two belonged to the GH3 family and one belonged to the GH1 family. Homology models of these proteins predicted a deep and narrow active site for the GH3 β-glucosidases (PfBgl3A and PfBgl3B) and a shallow open active site for the GH1 β-glucosidase (PfBgl1A). The enzymatic assays indicated that P. funiculosum-secreted proteins showed high β-glucosidase activities with prominent bands on the 4-methylumbelliferyl β-D-glucopyranoside zymogram. To understand the contributory effects of each of the three secreted β-glucosidases (PfBgls), the corresponding gene was deleted separately, and the effect of the deletion on the β-glucosidase activity of the secretome was examined. Although not the most abundant, PfBgl3A was found to be one of the most important β-glucosidases, as evidenced by a 42% reduction in β-glucosidase activity in the ΔPfBgl3A strain. Our results advance the understanding of the genetic and biochemical nature of all β-glucosidases produced by P. funiculosum and pave the way to design a superior biocatalyst for the hydrolysis of lignocellulosic biomass. IMPORTANCE Commercially available cellulases are primarily produced from Trichoderma reesei. However, external supplementation of the cellulase cocktail from this host with exogenous β-glucosidase is often required to achieve the desired optimal saccharification of cellulosic feedstocks. This challenge has led to the exploration of other cellulase-producing strains. The nonmodel hypercellulolytic fungus Penicillium funiculosum has been studied in recent times and identified as a promising source of industrial cellulases mainly due to its ability to produce a balanced concoction of cellulolytic enzymes, including β-glucosidases. Various genetic interventions targeted at strain improvement for cellulase production have been performed; however, the β-glucosidases of this strain have remained largely understudied. This study, therefore, reports profiling of all eight β-glucosidases of P. funiculosum via molecular and computational approaches. The results of this study provide useful insights that will establish the background for future engineering strategies to transform this fungus into an industrial workhorse.

Production, concentration and partial characterization of an enzymatic extract produced by an Aspergillus niger mutant in solid state fermentation

An enzymatic extract from Aspergillus niger 3T5B8 was produced by Solid State Fermentation (SSF) in aerated columns, using wheat bran as substrate. A combination of extracts produced using three different process conditions varying temperature, pH and aeration formed the final extract (Mixture). The Mixture was concentrated by an ultrafiltration process that partially purified and provided an efficient recovery of the enzymatic activities of xylanase (88.89%), polygalacturonase (89.3%), β-glucosidase (93.15%), protease (98.68%) and carboxymethylcellulase (CMCase) (98.93%). SDS-PAGE analysis showed 15 visible protein bands in the crude and concentrated Mixture with molecular weights ranging from 15.1 to 104.6 kDa. Thin layer chromatography confirmed the effective action of β-glucosidase and xylanase hydrolysis activities over cellobiose and xylan, respectively. A central composite design (CCD) with two variables and four replicates at the center points was used to determine the optimal temperature and pH for CMCase and β-glucosidase. The optimal temperature was 78.9 °C and pH 3.8 for CMCase and 52.8 °C and pH 4.8 for β-glucosidase, respectively.

Oxic and Anoxic Organic Polymer Degradation Potential of Endophytic Fungi From the Marine Macroalga, Ecklonia radiata

Cellulose and chitin are the most abundant polymeric, organic carbon source globally. Thus, microbes degrading these polymers significantly influence global carbon cycling and greenhouse gas production. Fungi are recognized as important for cellulose decomposition in terrestrial environments, but are far less studied in marine environments, where bacterial organic matter degradation pathways tend to receive more attention. In this study, we investigated the potential of fungi to degrade kelp detritus, which is a major source of cellulose in marine systems. Given that kelp detritus can be transported considerable distances in the marine environment, we were specifically interested in the capability of endophytic fungi, which are transported with detritus, to ultimately contribute to kelp detritus degradation. We isolated 10 species and two strains of endophytic fungi from the kelp Ecklonia radiata. We then used a dye decolorization assay to assess their ability to degrade organic polymers (lignin, cellulose, and hemicellulose) under both oxic and anoxic conditions and compared their degradation ability with common terrestrial fungi. Under oxic conditions, there was evidence that Ascomycota isolates produced cellulose-degrading extracellular enzymes (associated with manganese peroxidase and sulfur-containing lignin peroxidase), while Mucoromycota isolates appeared to produce both lignin and cellulose-degrading extracellular enzymes, and all Basidiomycota isolates produced lignin-degrading enzymes (associated with laccase and lignin peroxidase). Under anoxic conditions, only three kelp endophytes degraded cellulose. We concluded that kelp fungal endophytes can contribute to cellulose degradation in both oxic and anoxic environments. Thus, endophytic kelp fungi may play a significant role in marine carbon cycling via polymeric organic matter degradation.

Why Are Wet Wipes So Difficult to Preserve? Understanding the Intrinsic Causes

Over the last two decades, significant advances have been made in developing disposable baby wet wipes. Wet wipes consist of two main components: nonwoven fabric and liquid. Being more than 90% water, wet wipes are more susceptible to microbial growth than typical personal care products; hence, high concentrations of preservative compounds are often used to ensure extended protection against contamination. However, there is an obvious tendency to minimize the concentration of irritating actives. Baby wet wipes should contain particularly mild surfactants, well-tolerated preservatives, and a buffer system maintaining the formulation pH at a suitable level for the infant’s skin. Efforts have been centered on removing ingredients with irritation potential, such as phenoxyethanol. In addition, a move towards more natural fabrics is occurring. However, these modifications provoke new challenges in preserving the final products. The nature and composition of the fiber can influence the interactions between the preservative and the wipe, subsequently affecting the performance of the preservative system. In this study, we analyzed the causes of the challenge in preserving wet wipes. We found that fabrics containing natural fibers are the main source of contamination, promoting the generation of biofilms on their surfaces. Moreover, the hydrophilic–lipophilic balance (HLB) was utilized to rationalize the physicochemical interactions between the fabric and the preservatives.

Thermostable cellulose saccharifying microbial enzymes: Characteristics, recent advances and biotechnological applications

Cellulases play a promising role in the bioconversion of renewable lignocellulosic biomass into fermentable sugars which are subsequently fermented to biofuels and other value-added chemicals. Besides biofuel industries, they are also in huge demand in textile, detergent, and paper and pulp industries. Low titres of cellulase production and processing are the main issues that contribute to high enzyme cost. The success of ethanol-based biorefinery depends on high production titres and the catalytic efficiency of cellulases functional at elevated temperatures with acid/alkali tolerance and the low cost. In view of their wider application in various industrial processes, stable cellulases that are active at elevated temperatures in the acidic-alkaline pH ranges, and organic solvents and salt tolerance would be useful. This review provides a recent update on the advances made in thermostable cellulases. Developments in their sources, characteristics and mechanisms are updated. Various methods such as rational design, directed evolution, synthetic & system biology and immobilization techniques adopted in evolving cellulases with ameliorated thermostability and characteristics are also discussed. The wide range of applications of thermostable cellulases in various industrial sectors is described.

Enzymatic activities and analysis of a mycelium-based composite formation using peach palm (Bactris gasipaes) residues on Lentinula edodes

By seeding fungus on top of industry residues, a mycelium can grow and form a compact network structure; however, it may not develop due to lack of optimal nutrients from the substrate. Consequently, peach-palm residues can be a potential alternative; so, to test this hypothesis, this work evaluates the effect of peach-palm residues as substrate for the growth of mycelium based on Lentinula edodes. They were also supplemented with cassava bran and various sources of nitrogen-ammonium sulphate, potassium nitrate, and soy flour—to analyse its effects on its physico-chemical, enzymatic activities, and thermal and mechanical properties of the final composite at 12 and 20 days of cultivation. This mycelium was able to grow at optimum source treatment conditions, which depends on the ratio of Carbon to Nitrogen, within only 12 days of inoculation. Furthermore, the enzyme activities directly correlate with the mycelium growth with optimum conditions of pH, water activity, and moisture for L. edodes to grow having lower enzyme activities for a well-developed composite; whereas higher activities were seen for a weakly developed material, and this material demonstrates mechanical and thermal properties similar to common mycelium-based composites. Therefore, this work demonstrates that peach-palm residues can be a potential alternative for mycelium-based composite.

Genome and secretome analysis of jute endophyte Grammothele lineata strain SDL-CO-2015-1: Insights into its lignocellulolytic structure and secondary metabolite profile

Grammothele lineata strain SDL-CO-2015-1, jute (Corchorus olitorius) endophyte has been reported to produce anti-cancer drug paclitaxel in culture condition. Here we investigated the genome using different bioinformatic tools to find its association with the production of commercially important compounds including taxol. Carbohydrate-active enzymes, proteases, and secretory proteins were annotated revealing a complex endophytic relationship with its plant host. The presences of a diverse range of CAZymes including numerous lignocellulolytic enzymes support its potentiality in biomass degradation. Genome annotation led to the identification of 28 clusters for secondary metabolite biosynthesis. Several biosynthesis gene clusters were identified for terpene biosynthesis from antiSMASH analysis but none could be specifically pinned to taxol synthesis. This study will direct us to understand the genomic organization of endophytic basidiomycetes with a potential for producing numerous commercially important enzymes and secondary metabolites taking G. lineata as a model.

Influence of nitrogen sources on the enzymatic activity and grown by Lentinula edodes in biomass Eucalyptus benthamii

Lignocellulose is the most abundant environmental component and a renewable organic resource in soil. There are some filamentous fungi which developed the ability to break down and use cellulose, hemicellulose and lignin as an energy source. The objective of this research was to analyze the effect of three nitrogen resources (ammonium sulfate, saltpetre, soybean) in the holocellulolitic activity of Lentinula edodes EF 50 using as substrate sawdust E. benthamii. An experimental design mixture was applied with repetition in the central point consisting of seven treatments (T) of equal concentrations of nitrogen in ammonium sulfate, potassium nitrate and soybean. The enzymatic activity of avicelase, carboxymetilcellulase, β-glucosidase, xylanases and manganese peroxidase was determined. The humidity, pH, water activity (aw) and qualitative analysis of mycelial growth in 8 times of cultivation were evaluated. The results showed negative effect on enzyme production in treatments with maximum concentration of ammonium sulfate and potassium nitrate. The treatments with cooked soybean flour expressed higher enzymatic activities in times of 3, 6 and 9 days of culture, except in the activity of manganese peroxidase. The highest production was observed in the treatment with ammonium sulfate, and soybean (83.86 UI.L-1) at 20 days of cultivation.

Saccharification of rice straw by cellulase from a local Trichoderma harzianum SNRS3 for biobutanol production

BACKGROUND

Rice straw has shown to be a promising agricultural by-product in the bioconversion of biomass to value-added products. Hydrolysis of cellulose, a main constituent of lignocellulosic biomass, is a requirement for fermentable sugar production and its subsequent bioconversion to biofuels such as biobutanol. The high cost of commercial enzymes is a major impediment to the industrial application of cellulases. Therefore, the use of local microbial enzymes has been suggested. Trichoderma harzianum strains are potential CMCase and β-glucosidase producers. However, few researches have been reported on cellulase production by T. harzianum and the subsequent use of the crude cellulase for cellulose enzymatic hydrolysis. For cellulose hydrolysis to be efficiently performed, the presence of the whole set of cellulase components including exoglucanase, endoglucanase, and β-glucosidase at a considerable concentration is required. Biomass recalcitrance is also a bottleneck in the bioconversion of agricultural residues to value-added products. An effective pretreatment could be of central significance in the bioconversion of biomass to biofuels.

RESULTS

Rice straw pretreated using various concentrations of NaOH was subjected to enzymatic hydrolysis. The saccharification of rice straw pretreated with 2% (w/v) NaOH using crude cellulase from local T. harzianum SNRS3 resulted in the production of 29.87 g/L reducing sugar and a yield of 0.6 g/g substrate. The use of rice straw hydrolysate as carbon source for biobutanol fermentation by Clostridium acetobutylicum ATCC 824 resulted in an ABE yield, ABE productivity, and biobutanol yield of 0.27 g/g glucose, 0.04 g/L/h and 0.16 g/g glucose, respectively. As a potential β-glucosidase producer, T. harzianum SNRS3 used in this study was able to produce β-glucosidase at the activity of 173.71 U/g substrate. However, for cellulose hydrolysis to be efficient, Filter Paper Activity at a considerable concentration is also required to initiate the hydrolytic reaction. According to the results of our study, FPase is a major component of cellulose hydrolytic enzyme complex system and the reducing sugar rate-limiting enzyme.

CONCLUSION

Our study revealed that rice straw hydrolysate served as a potential substrate for biobutanol production and FPase is a rate-limiting enzyme in saccharification.

Degradation of oxo-biodegradable plastic by Pleurotus ostreatus

Growing concerns regarding the impact of the accumulation of plastic waste over several decades on the environmental have led to the development of biodegradable plastic. These plastics can be degraded by microorganisms and absorbed by the environment and are therefore gaining public support as a possible alternative to petroleum-derived plastics. Among the developed biodegradable plastics, oxo-biodegradable polymers have been used to produce plastic bags. Exposure of this waste plastic to ultraviolet light (UV) or heat can lead to breakage of the polymer chains in the plastic, and the resulting compounds are easily degraded by microorganisms. However, few studies have characterized the microbial degradation of oxo-biodegradable plastics. In this study, we tested the capability of Pleurotus ostreatus to degrade oxo-biodegradable (D₂W) plastic without prior physical treatment, such as exposure to UV or thermal heating. After 45 d of incubation in substrate-containing plastic bags, the oxo-biodegradable plastic, which is commonly used in supermarkets, developed cracks and small holes in the plastic surface as a result of the formation of hydroxyl groups and carbon-oxygen bonds. These alterations may be due to laccase activity. Furthermore, we observed the degradation of the dye found in these bags as well as mushroom formation. Thus, P. ostreatus degrades oxo-biodegradable plastics and produces mushrooms using this plastic as substrate.

Thin film of lignocellulosic nanofibrils with different chemical composition for QCM-D study

Thin films of lignocellulosic nanofibrils (LCNFs) with different chemical compositions were prepared for real-time observation of their enzymatic adsorption and degradation behavior by using a quartz crystal microbalance with dissipation monitoring (QCM-D). LCNFs were obtained by disk milling followed by high-pressure homogenization of Hinoki cypress. The lignin contents were adjusted by the sodium chlorite treatment. The film thickness was adjusted by controlling the concentration of the LCNF suspension, which was determined from its proportional relationship to the UV absorbance of lignin. The enzymatic degradation behavior was investigated with a commercial enzyme mixture. The results of the QCM-D showed that changes in frequency and dissipation in the initial reaction stage were different from the typical changes reported for pure cellulose. To the best of our knowledge, this is the first report of the preparation of thin films of LCNFs with high lignin and hemicellulose contents and their application in a QCM-D study.

Construction of a chimeric thermoacidophilic beta-endoglucanase

Background

The archeaon Sulfolobus solfataricus P2 encodes a thermoacidophilic cellulase which shows an extreme acid and thermal stability with a pH optimum at 1.8 and a temperature optimum at 80°C. This extraordinary enzyme could be useful for biotechnological exploitation but the expression and purification in expression hosts like E. coli is unsatisfactory due to the high aggregation tendency of the recombinant enzyme. The thermophilic cellulase CelA from Thermotoga maritima belongs to the same glycoside hydrolase family (GH12) but has a neutral pH optimum. In contrast to SSO1949 this enzyme is expressed partially soluble in E. coli.

Results

We aimed to constructed a hybrid enzyme based on these two beta-endoglucanases which should successfully combine the advantageous properties of both cellulases, i.e. recombinant expression in E. coli, acidophily and thermophily. We constructed two hybrid proteins after bioinformatic analysis: both hybrids are expressed insoluble in E. coli, but one hybrid enzyme was successfully refolded from washed inclusion bodies.

Conclusions

The refolded active chimeric enzyme shows a temperature optimum of approximately 85°C and a pH optimum of approximately pH 3 thus retaining the advantageous properties of the Sulfolobus parent enzyme. This study suggests that the targeted construction of chimeric enzymes is an alternative to point mutational engineering efforts as long as parent enzymes with the wanted properties are available.

Cellulase production by Penicillium funiculosum and its application in the hydrolysis of sugar cane bagasse for second generation ethanol production by fed batch operation

This study aimed to produce a cellulase blend and to evaluate its application in a simultaneous saccharification and fermentation (SSF) process for second generation ethanol production from sugar cane bagasse. The sugar cane bagasse was subjected to pretreatments (diluted acid and alkaline), as for disorganizing the ligocellulosic complex, and making the cellulose component more amenable to enzymatic hydrolysis. The residual solid fraction was named sugar cane bagasse partially delignified cellulignin (PDC), and was used for enzyme production and ethanol fermentation. The enzyme production was performed in a bioreactor with two inoculum concentrations (5 and 10% v/v). The fermentation inoculated with higher inoculum size reduced the time for maximum enzyme production (from 72 to 48). The enzyme extract was concentrated using tangential ultrafiltration in hollow fiber membranes, and the produced cellulase blend was evaluated for its stability at 37 °C, operation temperature of the simultaneous SSF process, and at 50 °C, optimum temperature of cellulase blend activity. The cellulolytic preparation was stable for at least 300 h at both 37 °C and 50 °C. The ethanol production was carried out by PDC fed-batch SSF process, using the onsite cellulase blend. The feeding strategy circumvented the classic problems of diffusion limitations by diminishing the presence of a high solid:liquid ratio at any time, resulting in high ethanol concentration at the end of the process (100 g/L), which corresponded to a fermentation efficiency of 78% of the maximum obtainable theoretically. The experimental results led to the ratio of 380 L of ethanol per ton of sugar cane bagasse PDC.

Identifying and characterizing the most significant β-glucosidase of the novel species Aspergillus saccharolyticus

The newly discovered fungal species Aspergillus saccharolyticus was found to produce a culture broth rich in β-glucosidase activity. In this present work, the main β-glucosidase of A. saccharolyticus responsible for the efficient hydrolytic activity was identified, isolated, and characterized. Ion exchange chromatography was used to fractionate the culture broth, yielding fractions with high β-glucosidase activity and only 1 visible band on an SDS–PAGE gel. Mass spectrometry analysis of this band gave peptide matches to β-glucosidases from aspergilli. Through a polymerase chain reaction approach using degenerate primers and genome walking, a 2919 bp sequence encoding the 860 amino acid BGL1 polypeptide was determined. BGL1 of A. saccharolyticus has 91% and 82% identity with BGL1 from Aspergillus aculeatus and BGL1 from Aspergillus niger , respectively, both belonging to Glycoside Hydrolase family 3. Homology modeling studies suggested β-glucosidase activity with preserved retaining mechanism and a wider catalytic pocket compared with other β-glucosidases. The bgl1 gene was heterologously expressed in Trichoderma reesei QM6a, purified, and characterized by enzyme kinetics studies. The enzyme can hydrolyze cellobiose, p-nitrophenyl-β-d-glucoside, and cellodextrins. The enzyme showed good thermostability, was stable at 50 °C, and at 60 °C it had a half-life of approximately 6 h.

Isolation of Cellulolytic Bacillus subtilis Strains from Agricultural Environments

The bioconversion of cellulose and hemicellulose to soluble sugars is important for global stabilization and a sustainable human society. Here, hundreds of cellulolytic bacteria were screened and isolated from soil, compost, and animal waste slurry in Jeju Island, South Korea. Among the isolates, three strains, SL9-9, C5-16, and S52-2, showing higher potential for practical uses were purified on carboxymethyl cellulose (CMC) agar plates and identified as Bacillus subtilis strains by morphological, physiological, and biochemical characterization and 16S rRNA gene analysis. The production patterns of cellulose or hemicellulose-degrading enzymes were investigated during cell culture. All three isolated strains produced CMCase, Avicelase, β-glucosidase, and xylanase enzymes, which suggested synergic cellulolytic systems in Bacillus subtilis. The enzymes showing CMCase, Avicelase, and xylanase activities existed in cell-free culture supernatant, meanwhile β-glucosidase activity was detected in cell debris suggesting that three of the enzymes, including CMCase, Avicelase, and xylanase, were extracellular, and β-glucosidase was cell membrane bound. The three isolates, SL9-9, C5-16, and S52-2, were not the same strains, presenting slight differences in biochemical characteristics, 16S rRNA gene sequences, and cellulolytic enzyme activities.

Inactivation of shiga toxin-producing Escherichia coli (STEC) and degradation and removal of cellulose from STEC surfaces by using selected enzymatic and chemical treatments

Some Shiga toxin-producing Escherichia coli (STEC) strains produce extracellular cellulose, a long polymer of glucose with β-1-4 glycosidic bonds. This study evaluated the efficacies of selected enzymatic and chemical treatments in inactivating STEC and degrading/removing the cellulose on STEC surfaces. Six cellulose-producing STEC strains were treated with cellulase (0.51 to 3.83 U/15 ml), acetic and lactic acids (2 and 4%), as well as an acidic and alkaline sanitizer (manufacturers' recommended concentrations) under appropriate conditions. Following each treatment, residual amounts of cellulose and surviving populations of STEC were determined. Treatments with acetic and lactic acids significantly (P < 0.05) reduced the populations of STEC, and those with lactic acid also significantly decreased the amounts of cellulose on STEC. The residual amounts of cellulose on STEC positively correlated to the surviving populations of STEC after the treatments with the organic acids (r = 0.64 to 0.94), and the significance of the correlations ranged from 83 to 99%. Treatments with cellulase and the sanitizers both degraded cellulose. However, treatments with cellulase had no influence on the fate of STEC, and those with the sanitizers reduced STEC cell populations to undetectable levels. Thus, the correlations between the residual amounts of cellulose and the surviving populations of STEC caused by these two treatments were not observed. The results suggest that the selected enzymatic and chemical agents degraded and removed the cellulose on STEC surfaces, and the treatments with organic acids and sanitizers also inactivated STEC cells. The amounts of cellulose produced by STEC strains appear to affect their susceptibilities to certain sanitizing treatments.

Use of hemicellulose hydrolysate for beta-glucosidase fermentation

Hydrolysis of cellulose by Trichoderma cellulases often results in a mixture of glucose, cellobiose, and low-mol-wt cellodextrins. Cellobiose is nonfermentable for most yeasts, and therefore it has to be hydrolyzed to glucose by beta-glucosidase prior to ethanol fermentation. In the present study, the beta-glucosidase production of one Penicillium and three Aspergillus strains, which were previously selected out of 24 strains, was investigated on steam pretreated willow. Both steam-pretreated willow and hemicellulose hydrolysate, released during steam explosion of willow, were used as carbon sources. Reference cultivation runs were performed using prehydrolyzed Solka Floc and glucose. The four strains were compared with Trichoderma reesei regarding sugar consumption and beta-glucosidase production. Aspergillus niger and Aspergillus phoenicis proved to be the best enzyme producers on hemicellulose hydrolysate. The maximum beta-glucosidase activity, 4.60 IU/mL, was obtained when A. phoenicis was cultivated on the mixture of hemicellulose hydrolysate and steam-pretreated willow. The maximum yield of enzyme activity, 502 IU/g total carbohydrate, was obtained when Aspergillus foetidus was cultivated on the hemicellulose hydrolysate.

Production and distribution of beta-glucosidase in a mutant strain Trichoderma viride T 100-14

The characterization of beta-glucosidase's production and distribution in a mutant strain Trichoderma viride T 100-14 at extracellular and intracellular levels were studied in this paper. Three experiment groups were done automatically with pH controlled at 4.8 during fermentation process, with 1mg/ml 2-deoxy-d-glucose addition or without pH control and 2-deoxy-d-glucose addition (control). Activity assay and electron microscopic immunogold labeling experiments were performed at different culture periods (24, 48, 72, 96 and 120 hours). Under constant pH 4.8, high density of immunogold labeling particles, highest intracellular enzyme activity, total enzyme activity and specific activity were observed at 24 hours of fermentation. After 72 hours, the extracellular and total activities fluctuated little and the maximal activity in extracellular fraction was 2.7 times higher than control. By contrast, with 2-deoxy-d-glucose addition, the secreted and total beta-glucosidase activities achieved their maximum at 96 hours of fermentation, and the maximal secreted activity increased 2.05-fold than the control. Additionally, the secretion ratio (maximal secreted beta-glucosidase activity/maximal total activity) with pH control or 2-deoxy-d-glucose addition was elevated profoundly near to a level as the cellulase in fungi.

Cyclic AMP regulates the biosynthesis of cellobiohydrolase in Cellulomonas flavigena growing in sugar cane bagasse

Cellulomonas flavigena produces a battery of cellulase components that act concertedly to degrade cellulose. The addition of cAMP to repressed C. flavigena cultures released catabolic repression, while addition of cAMP to induced C. flavigena cultures led to a cellobiohydrolase hyperproduction. Exogenous cAMP showed positive regulation on cellobiohydrolase production in C. flavigena grown on sugar cane bagasse. A C. flavigena cellobiohydrolase gene was cloned (named celA), which coded for a 71- kDa enzyme. Upstream, a repressor celR1, identified as a 38 kDa protein, was monitored by use of polyclonal antibodies.

Diversity and activity of cellulose-decomposing bacteria, isolated from a sandy and a loamy soil after long-term manure application

The community of culturable cellulolytic bacteria was analyzed in two long-term experimental field sites on Albic Luvisol (silty sand) and Haplic Phaeozem (loam), with and without farmyard manure treatment. Against the backdrop of significant differences in soil properties, the bacterial community structure differed clearly between sites and was affected by manure application as analyzed by T-RFLP of 16S rDNA. The population densities of cellulolytic bacteria were significantly increased by manure application in Phaeozem. Cellulose decomposing potentials of 537 isolates were tested on soluble, colloidal, and crystalline cellulose. The results showed some evidence of a greater proportion of isolates with high decomposition activity in Luvisol, but no impact from manure application could be observed in both soils. Restriction analysis and sequencing of 16S rDNA of isolates revealed a rather simple community composition that was dominated by Streptomyces (67%). The composition of the RFLP groups was affected by manure application, which was most evident in Luvisol, whereas an effect of the soil type could not be found. Although abundant RFLP groups were assigned to phylogenetically different bacterial classes (Actinobacteria, Betaproteobacteria, and Gammaproteobacteria), cellulolytic activity could not consistently be differentiated. All in all, cellulolytic capabilities of the isolates were highly variable and did not map to phylogenetic affiliation.

Isolation of cellulolytic enzymes from moldy silage by new culture-independent strategy

A culture-independent strategy has been developed for investigation of cellulases in moldy silage. By the qualitative differences in the adsorption of cellulases on lingo-cellulosics, a new cellobiohydrolase (CBH) with apparent molecular mass of 194 kDa was isolated and characterized. The entire extracellular proteins of silage were separated by two-dimensional gel electrophoresis, and five potential endoglucanases were identified by activity staining. These results demonstrate the feasibility of direct screening cellulases from environment without microorganism cultivation and this strategy could be expected to facilitate the research of uncultured microorganisms.

Potential and utilization of thermophiles and thermostable enzymes in biorefining

In today's world, there is an increasing trend towards the use of renewable, cheap and readily available biomass in the production of a wide variety of fine and bulk chemicals in different biorefineries. Biorefineries utilize the activities of microbial cells and their enzymes to convert biomass into target products. Many of these processes require enzymes which are operationally stable at high temperature thus allowing e.g. easy mixing, better substrate solubility, high mass transfer rate, and lowered risk of contamination. Thermophiles have often been proposed as sources of industrially relevant thermostable enzymes. Here we discuss existing and potential applications of thermophiles and thermostable enzymes with focus on conversion of carbohydrate containing raw materials. Their importance in biorefineries is explained using examples of lignocellulose and starch conversions to desired products. Strategies that enhance thermostablity of enzymes both in vivo and in vitro are also assessed. Moreover, this review deals with efforts made on developing vectors for expressing recombinant enzymes in thermophilic hosts.

Outlook for cellulase improvement: screening and selection strategies

Cellulose is the most abundant renewable natural biological resource, and the production of biobased products and bioenergy from less costly renewable lignocellulosic materials is important for the sustainable development of human beings. A reduction in cellulase production cost, an improvement in cellulase performance, and an increase in sugar yields are all vital to reduce the processing costs of biorefineries. Improvements in specific cellulase activities for non-complexed cellulase mixtures can be implemented through cellulase engineering based on rational design or directed evolution for each cellulase component enzyme, as well as on the reconstitution of cellulase components. Here, we review quantitative cellulase activity assays using soluble and insoluble substrates, and focus on their advantages and limitations. Because there are no clear relationships between cellulase activities on soluble substrates and those on insoluble substrates, soluble substrates should not be used to screen or select improved cellulases for processing relevant solid substrates, such as plant cell walls. Cellulase improvement strategies based on directed evolution using screening on soluble substrates have been only moderately successful, and have primarily targeted improvement in thermal tolerance. Heterogeneity of insoluble cellulose, unclear dynamic interactions between insoluble substrate and cellulase components, and the complex competitive and/or synergic relationship among cellulase components limit rational design and/or strategies, depending on activity screening approaches. Herein, we hypothesize that continuous culture using insoluble cellulosic substrates could be a powerful selection tool for enriching beneficial cellulase mutants from the large library displayed on the cell surface.

Toward an aggregated understanding of enzymatic hydrolysis of cellulose: noncomplexed cellulase systems

Information pertaining to enzymatic hydrolysis of cellulose by noncomplexed cellulase enzyme systems is reviewed with a particular emphasis on development of aggregated understanding incorporating substrate features in addition to concentration and multiple cellulase components. Topics considered include properties of cellulose, adsorption, cellulose hydrolysis, and quantitative models. A classification scheme is proposed for quantitative models for enzymatic hydrolysis of cellulose based on the number of solubilizing activities and substrate state variables included. We suggest that it is timely to revisit and reinvigorate functional modeling of cellulose hydrolysis, and that this would be highly beneficial if not necessary in order to bring to bear the large volume of information available on cellulase components on the primary applications that motivate interest in the subject.

β-Glucosidase activity from the thermophilic fungusScytalidium thermophilumis stimulated by glucose and xylose

An inducible mycelial beta-glucosidase from Scytalidum thermophilum was characterized. The enzyme exhibited a pI of 6.5, a carbohydrate content of 15%, and an apparent molecular mass of about 40 kDa. Optima of temperature and pH were 60 degrees C and 6.5, respectively. The enzyme was stable up to 1 h at 50 degrees C and exhibited a half-life of 20 min at 55 degrees C. The enzyme hydrolyzed p-nitrophenyl-beta-d-glucopyranoside, p-nitrophenyl-beta-d-xylopyranoside, o-nitrophenyl-beta-d-galactopyranoside, p-nitrophenyl-alpha-arabinopyranoside, cellobiose, laminaribiose and lactose. Kinetic studies indicated that the same enzyme hydrolyzed these substrates. Beta-Glucosidase was activated by glucose or xylose at concentration varying from 50 to 200 mM. The apparent affinity constants (K0.5) for glucose and xylose were 36.69 and 43.24 mM, respectively. The stimulatory effect of glucose and xylose on the S. thermophilum beta-glucosidase is a novel characteristic which distinguish this enzyme from all other beta-glucosidases so far described.

Cellulose-degrading potentials and phylogenetic classification of carboxymethyl-cellulose decomposing bacteria isolated from soil

In a previous study, culturable carboxymethyl-cellulose (CMC) decomposing soil bacteria isolated from different sampling positions across an agricultural encatchment have been classified into 31 pattern groups by digestion of amplified 16S rDNA using a single restriction enzyme (Ulrich and Wirth: Microb. Ecol. 37, 238-247, 1999). In order to reveal relationships between phylogenetic diversity and phenotypic functions, a further differentiation of two selected site-specific pattern groups (I and H) was performed, resulting in a sub-classification of four and three ARDRA groups, respectively. Based on sequencing a representative isolate of each ARDRA group, the isolates were assigned to the genus Streptomyces. The ARDRA groups were dispersed across various clades of the genus with a direct affiliation to species known for cellulolytic activity in one group, only. The isolates differed in potentials to degrade colloidal, native or highly crystalline cellulose derivatives. Out of 39 isolates, 11 were capable of degrading all substrates, 17 were restricted to degrade CMC only, and 11 were active decomposers of exclusively both CMC and colloidal cellulose. In most cases, the genetic classification of the isolates corresponded with groupings based on cellulose degrading capabilities. Thus, isolates of four ARDRA groups were restricted to the degradation of CMC, while two further isolates which efficiently degraded all cellulose derivatives formed two separate ARDRA groups. The major ARDRA group, however; displayed a high variability of degradation capabilities. The study of additional phenotypic features revealed a broad potential to decompose a set of various carbon substrates, which matched the phylogenetic classification in several cases.

Extracellular beta-D-glucosidase from Chaetomium thermophilum var. coprophilum: production, purification and some biochemical properties

The thermophilic fungus Chaetomium thermophilum var. coprophilum produced large amounts of extracellular and intracellular beta-glucosidase activity when grown on cellulose or cellobiose as carbon sources. The presence of glucose in the culture medium drastically decreased the level of beta-glucosidase activity, while cycloheximide prevented the induction of the extracellular enzyme activity by cellobiose. An extracellular beta-glucosidase induced by avicel was purified by a procedure involving acetone precipitation and chromatography on two DEAE-cellulose columns. The purified enzyme was a basic protein, with a carbohydrate content of 73%. The deglycosylated enzyme exhibited a molecular mass of 43 kDa, with pH and temperature optima of 5.5 and 65 degrees C respectively. The beta-glucosidase hydrolysed only cellobiose and p-nitrophenyl-beta-D-glucopyranoside, exhibiting apparent Km values of 3.13 mM and 0.76 mM, respectively. The native purified enzyme was stable up to 2 hours at 60 degrees C, and its thermal stability was directly dependent on glycosylation.

Microbial cellulose utilization: fundamentals and biotechnology

Fundamental features of microbial cellulose utilization are examined at successively higher levels of aggregation encompassing the structure and composition of cellulosic biomass, taxonomic diversity, cellulase enzyme systems, molecular biology of cellulase enzymes, physiology of cellulolytic microorganisms, ecological aspects of cellulase-degrading communities, and rate-limiting factors in nature. The methodological basis for studying microbial cellulose utilization is considered relative to quantification of cells and enzymes in the presence of solid substrates as well as apparatus and analysis for cellulose-grown continuous cultures. Quantitative description of cellulose hydrolysis is addressed with respect to adsorption of cellulase enzymes, rates of enzymatic hydrolysis, bioenergetics of microbial cellulose utilization, kinetics of microbial cellulose utilization, and contrasting features compared to soluble substrate kinetics. A biological perspective on processing cellulosic biomass is presented, including features of pretreated substrates and alternative process configurations. Organism development is considered for "consolidated bioprocessing" (CBP), in which the production of cellulolytic enzymes, hydrolysis of biomass, and fermentation of resulting sugars to desired products occur in one step. Two organism development strategies for CBP are examined: (i) improve product yield and tolerance in microorganisms able to utilize cellulose, or (ii) express a heterologous system for cellulose hydrolysis and utilization in microorganisms that exhibit high product yield and tolerance. A concluding discussion identifies unresolved issues pertaining to microbial cellulose utilization, suggests approaches by which such issues might be resolved, and contrasts a microbially oriented cellulose hydrolysis paradigm to the more conventional enzymatically oriented paradigm in both fundamental and applied contexts.

The structure of Rhodothermus marinus Cel12A, a highly thermostable family 12 endoglucanase, at 1.8 A resolution

Cellulose is one of the most abundant polysaccharides in nature and microorganisms have developed a comprehensive system for enzymatic breakdown of this ubiquitous carbon source, a subject of much interest in the biotechnology industry. Rhodothermus marinus produces a hyperthermostable cellulase, with a temperature optimum of more than 90 degrees C, the structure of which is presented here to 1.8 A resolution. The enzyme has been classified into glycoside hydrolase family 12; this is the first structure of a thermophilic member of this family to have been solved. The beta-jelly roll fold observed has identical topology to those of the two mesophilic members of the family whose structures have been elucidated previously. A Hepes buffer molecule bound in the active site may have triggered a conformational change to an active configuration as the two catalytic residues Glu124 and Glu207, together with dependent residues, are observed in a conformation similar to that seen in the structure of Streptomyces lividans CelB2 complexed with an inhibitor. The structural similarity between this cellulase and the mesophilic enzymes serves to highlight features that may be responsible for its thermostability, chiefly an increase in ion pair number and the considerable stabilisation of a mobile region seen in S. lividans CelB2. Additional aromatic residues in the active site region may also contribute to the difference in thermophilicity.

Purification and characterization of cellulases produced by two Bacillus strains

Cellulases produced by two Bacillus strains, CH43 and HR68, isolated from hot springs in Zimbabwe, were purified to homogeneity from culture supernatants. Both enzymes had molecular mass of 40 kDa and isoelectric point of 5.4. The enzymes also resembled each other in N-terminal amino acid sequence which was Ala-Gly-Thr-Lys-Thr-Pro-Val-Ala-Lys-Asn-Gly-Gln, showing 100% homology with that of endoglucanases from Bacillus subtilis belonging to glycoside hydrolase family five. The cellulases were optimally active in the pH range of 5-6.5. The optimum temperature was 65 and 70 degrees C for the endoglucanase of CH43 and HR68, respectively. The CH43 enzyme was stable at 50 degrees C in a pH range of 6-10, and HR68 at pH 6-8. Both the enzymes retained complete activity for at least 24 h at 50 degrees C. The enzymes showed highest activity with beta-glucan as substrate followed by carboxymethylcellulose. Significant activity was also observed with crystalline forms of cellulose such as filter paper and Avicel, particularly for HR68 cellulase. For carboxymethycellulose, the CH43 and HR68 cellulases had a Km of 1.5 and 1.7 mg ml(-1), respectively, and Vmax of 0.93 and 1.70 mmol glucose min(-1) mg protein(-1) respectively. The activity of the enzymes was not influenced by most metal ions at 1 mM concentration, but was increased by about 38% by Co2+. The inhibition by Hg2+ and Mn2+ was higher for CH43 than for HR68 enzyme. Ag+ inhibited the CH43 activity but stimulated the HR68 activity. The CH43 cellulase was inhibited by N-bromosuccinimide and iodoacetamide while HR68 was unaffected.

Cellobiose dehydrogenase from Phanerochaete chrysosporium is encoded by two allelic variants

The complete nucleotide sequences of two alleles of cellobiose dehydrogenase, cdh-1 (3,627 bp) and cdh-2 (3,623 bp), from Phanerochaete chrysosporium OGC101 are reported. The nucleotide sequences of cdh-1 and cdh-2 exhibit 97% similarity. A total of eighty-six point mutations between cdh-1 and cdh-2 are observed. Both alleles have 14 exons, and the introns are located at exactly the same positions. The translation products of these alleles have identical amino acid sequences. Restriction fragment length polymorphism analyses of homokaryotic derivatives show segregation of the CDH alleles.

Three-dimensional structures of three engineered cellulose-binding domains of cellobiohydrolase I from Trichoderma reesei

Three-dimensional solution structures for three engineered, synthetic CBDs (Y5A, Y31A, and Y32A) of cellobiohydrolase I (CBHI) from Trichoderma reesei were studied with nuclear magnetic resonance (NMR) and circular dichroism (CD) spectroscopy. According to CD measurements the antiparallel beta-sheet structure of the CBD fold was preserved in all engineered peptides. The three-dimensional NMR-based structures of Y31A and Y32A revealed only small local changes due to mutations in the flat face of CBD, which is expected to bind to crystalline cellulose. Therefore, the structural roles of Y31 and Y32 are minor, but their functional importance is obvious because these mutants do not bind strongly to cellulose. In the case of Y5A, the disruption of the structural framework at the N-terminus and the complete loss of binding affinity implies that Y5 has both structural and functional significance. The number of aromatic residues and their precise spatial arrangement in the flat face of the type I CBD fold appears to be critical for specific binding. A model for the CBD binding in which the three aligned aromatic rings stack onto every other glucose ring of the cellulose polymer is discussed.