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Oil impregnated cellulose paper (OIP) constitute major insulation of transformer windings. The cellulose insulation determines the lifespan of a transformer. Many of the transformer failures are mainly due to frequent application of over-voltages. It is necessary to analyze the degradation of OIP with respect to time interval between the impulse overvoltages. Cellulose degradation is usually characterized in terms of scission fraction which is given by degree of polymerization (DP). In this paper, an attempt has been made to analyze the degradation of OIP for different impulse voltages and time interval between the successive impulse voltages. Detailed experimental analyses are carried out for impulse overvoltages of 1.2/50µs, 0.4/50µs and 0.064/50µs by maintaining the time interval of 1 second, 3 seconds and 5 seconds between the successive impulses.

Background Degradation of cellulose to glucose requires the cooperative action of three classes of enzymes, collectively known as cellulases. Endoglucanases randomly bind to cellulose surfaces and generate new chain ends by hydrolyzing β-1,4-D-glycosidic bonds. Exoglucanases bind to free chain ends and hydrolyze glycosidic bonds in a processive manner releasing cellobiose units. Then, β-glucosidases hydrolyze soluble cellobiose to glucose. Optimal synergistic action of these enzymes is essential for efficient digestion of cellulose. Experiments show that as hydrolysis proceeds and the cellulose substrate becomes more heterogeneous, the overall degradation slows down. As catalysis occurs on the surface of crystalline cellulose, several factors affect the overall hydrolysis. Therefore, spatial models of cellulose degradation must capture effects such as enzyme crowding and surface heterogeneity, which have been shown to lead to a reduction in hydrolysis rates. Results We present a coarse-grained stochastic model for capturing the key events associated with the enzymatic degradation of cellulose at the mesoscopic level. This functional model accounts for the mobility and action of a single cellulase enzyme as well as the synergy of multiple endo- and exo-cellulases on a cellulose surface. The quantitative description of cellulose degradation is calculated on a spatial model by including free and bound states of both endo- and exo-cellulases with explicit reactive surface terms (e.g., hydrogen bond breaking, covalent bond cleavages) and corresponding reaction rates. The dynamical evolution of the system is simulated by including physical interactions between cellulases and cellulose. Conclusions Our coarse-grained model reproduces the qualitative behavior of endoglucanases and exoglucanases by accounting for the spatial heterogeneity of the cellulose surface as well as other spatial factors such as enzyme crowding. Importantly, it captures the endo-exo synergism of cellulase enzyme cocktails. This model constitutes a critical step towards testing hypotheses and understanding approaches for maximizing synergy and substrate properties with a goal of cost effective enzymatic hydrolysis.

Cellulose, the most abundant biopolymer on earth, is composed of β – 1,4 – linked glucose units, which in turn form a highly ordered crystalline structure that is insoluble and recalcitrant to degradation. It is the world’s most attractive, abundant and renewable energy resource, representing the bioconversion of carbon dioxide into green plants. Cellulosic biomass, such as agricultural and forestry residues, waste paper and industrial waste can therefore be used as an inexpensive and abundantly available source of sugar for fermentation into fuel ethanol. The combustion of biofuels releases carbon dioxide which is thus recycled and hence the use of these fuels in transportation provides an alternative to fossil fuels, solving many environmental problems. The ability to degrade crystalline cellulose seems to be restricted to a specialized group of microorganisms which includes for example Clostridium, Cellulomonas, Cytophaga, Trichoderma etc. Hence the aim of this project was to create BioBricks using different cellulases from cellulose degraders and express them in different expression hosts like Escherichia coli, Bacillus subtilis, Citrobacter freundii etc., using two different promoters, spac and lac. It was observed that the expression of Cytophaga hutchinsonii cellulases (CHU_2103 and CHU_2802) and dehydrogenases (CHU_1944 and CHU_2315) was toxic to the E. coli host for some unknown reason. Therefore it was decided to use cellulases from Cellulomonas fimi, which are well characterized. BioBricks of cellulases (cenA and cex) from C. fimi were introduced into different expression hosts. It was observed that under our experimental conditions Citrobacter freundii SBS197 gave the best results. Both Pspac and Plac were functional in this organism with expression being higher when Pspac was used. When E. coli JM109 was used as an expression host, activity was only detected when the lac promoter was used to control the expression. Although the expression was higher when E. coli JM109 (containing Plac) was used as an expression host, almost all of this activity was residing within the cells, whereas when C. freundii SBS197 was used as an expression host, considerable activity was detected in the surrounding medium, which is essential for cellulose degradation. Growth curve studies were done to see if heterologous cellulases enable the host to use cellulosic substrates as a source of carbon. It was observed that C. freundii SBS197 expressing cenA and cex was able to use filter paper and Avicel as a source of carbon with maximum growth of up to 8.8×108 cfu/ml and 1.2×109 cfu/ml respectively. This was about 2 – 5 fold higher when compared to the control (vector and/or negative) strains. Filter paper completely disappeared within 3 – 4 days when C. freundii SBS197 was used. Slight degradation was observed when E. coli JM109 was used but there was no physical degradation seen when B. subtilis 168 was used as an expression host. Hence it was concluded that heterologous cellulases impart to C. freundii SBS197 with the ability to use cellulosic substrates as a source of carbon. The maximum growth obtained using these cultures is to our knowledge higher than what has been reported so far for recombinant organisms expressing heterologous cellulases using cellulosic substrates as a source of carbon.

Currently available tools for studying plant litter decomposition and invertebrate consumption in aquatic ecosystems have at least 2 major limitations: 1) the difficulty of manipulating litter chemical composition to provide mechanistic insights into attributes of litter quality controlling decomposition rate, and 2) lack of a standardized litter that hampers comparisons of results among studies. These limitations point to a need for a standard litter surrogate with adjustable chemical composition. We propose using a decomposition and consumption tablet (DECOTAB) consisting of cellulose powder embedded in an agar matrix to evaluate decomposition and consumption rates in aquatic environments. We describe the preparation of DECOTABs and demonstrate some applications in laboratory microcosms and outdoor mesocosms. A leaf shredder, the isopod Asellus aquaticus, and a collector-gatherer, the nonbiting midge larva Chironomus riparius, readily consumed DECOTABs, leading to massive mass loss of the tablets within 21 d (90%). The isopod also consumed DECOTABs amended with extracts of riparian plants and soil to create a chemically complex source of organic matter. Our results highlight the potential utility of DECOTABs to assess invertebrate contributions to organic matter decomposition in aquatic systems. In the absence of invertebrates, exposure of basic and complex DECOTABs to microorganisms resulted in significant mass loss within 21 d (10-25%), and addition of an antibiotic and fungicide suppressed microbial decomposition, suggesting that the tablets are useful for studying microbial processes. Complex tablets decomposed faster than the basic tablets, a result illustrating the importance of chemical composition of organic material for microbial decomposers. DECOTABs are a novel, versatile tool for addressing long-standing questions in aquatic ecology and environmental assessment.

A three-stage continuous culture system was used to segregate the component physiological groups of an anaerobic cellobiose-degrading association enriched and isolated from a landfill site. The optimum temperatures for methanogenesis were 30-35°C, although differences apparent in Vessels B and C at lower temperatures suggested the presence of distinct populations in the two vessels. There was no evidence of thermophilic methanogenic activity. Sulphate-reducing bacterial (SRB) activity was less affected by temperature perturbation, and there was significant SRB activity at 55°C.

ACCELERATED AGING OF PAPERS OF PURE CELLULOSE - MECHANISM OF CELLULOSE DEGRADATION AND PAPER EMBRITTLEMENT

A cellulolytic bacterial strain, designated P118, isolated from the gut of the tropical fish Parotocinclus maculicauda was identified as belonging to the genus Paenibacillus based on phenotypic and chemotaxonomic characteristics and the 16S rRNA gene sequence. The novel strain was Gram-positive, spore-forming and rod-shaped. Catalase but not oxidase was produced. Carboxymethylcellulose was hydrolyzed but starch or gelatin was not. Acetoin production was negative whereas nitrate reduction and urease production were positive. Many carbohydrates served as carbon sources for growth. MK-7 was the predominant isoprenoid quinone. Anteiso-C15:0 (38.73%) and C16:0 (20.85%) were the dominant cellular fatty acids. Strain P118 was closely related to Paenibacillus amylolyticus NRRL NRS-290, P. pabuli HSCC 492, P. tundrae Ab10b, P. xylanexedens B22a, and P. tylopili MK2 with 98.3-98.8% 16S rRNA gene sequence similarity. The results presented here suggest that strain P118 represents a novel species of the genus Paenibacillus and it is a potential strain for further studies concerning its role in the production of industrially important products from cellulosic biomass.

This research project was designed to play a vital role in the development of low cost sugars from cellulosic biomass and contributing to the national effort to displace fossil fuel usage in the USA transportation sector. The goal was to expand the portfolio of cell wall degrading enzymes through innovative research at the nano-scale level, prospecting for novel cellulases and building a kinetic framework for the development of more effective enzymatic conversion processes. More precisely, the goal was to elucidate the molecular mechanisms for some cellulases that are very familiar to members of our research team and to investigate what we hope are novel cellulases or new enzyme combinations from the world of plant pathogenic fungi and bacteria. Hydrolytic activities of various cellulases and cellulase cocktails were monitored at the nanoscale of cellulose fibrils and the microscale of pretreated cellulose particles, and we integrated this insight into a heterogeneous reaction framework. The over-riding approach for this research program was the application of innovative and cutting edge optical and high-throughput screening and analysis techniques for observing how cellulases hydrolyze real substrates.

Thermophilic fungal cellulases are promising enzymes in protein engineering efforts aimed at optimizing industrial processes, such as biomass degradation and biofuel production. The cloning and expression in recent years of new cellulase genes from thermophilic fungi have led to a better understanding of cellulose degradation in these species. Moreover, crystal structures of thermophilic fungal cellulases are now available, providing insights into their function and stability. The present paper is focused on recent progress in cloning, expression, regulation, and structure of thermophilic fungal cellulases and the current research efforts to improve their properties for better use in biotechnological applications.

We examine the results of recent Kraft paper/natural ester fluid insulation system sealed tube aging studies. The initial rates of cellulose degradation of Kraft and thermally upgraded Kraft in mineral oil or natural esters are similar. Subsequent degradation in natural ester occurs at a slower rate. This appears to be true for both plain and thermally upgraded Kraft. Based on early sealed tube aging results, the insulation unit life of the natural ester/thermally upgraded Kraft insulation system is estimated to be 130°C. Accelerated aging of single phase distribution transformers filled with natural ester also show a reduction using a thermally upgraded Kraft/natural ester insulation system, meeting criteria for 120°C hottest spot temperature operation.

Thermomonospora curvata Henssen 1957 is the type species of the genus Thermomonospora. This genus is of interest because members of this clade are sources of new antibiotics, enzymes, and products with pharmacological activity. In addition, members of this genus participate in the active degradation of cellulose. This is the first complete genome sequence of a member of the family Thermomonosporaceae. Here we describe the features of this organism, together with the complete genome sequence and annotation. The 5,639,016 bp long genome with its 4,985 protein-coding and 76 RNA genes is a part of the Genomic Encyclopedia of Bacteria and Archaea project.

Use of crude oil derivatives such as diesel and gasoline is becoming unsuitable due to their detriment to environment and to the increasing worldwide energy demand which is driving crude oil reservoirs towards exhaustion. Replacement of diesel and gasoline with biofuels (i.e. biodiesel and bioethanol, respectively) is very desirable. In fact, biofuels are not only environmentally sustainable, but also potentially inexhaustible due to the large amounts of waste biomasses from which they can be retrieved. In the present study, a model compound (micro-crystalline cellulose) was dissolved in phosphoric acid and converted at 80 °C to glucose, thereby providing the possible substrate for fermentation to bioethanol. Results revealed that after 1 h heating, the reaction had the largest glucose yield as compared to similar studies done by using other acid catalysts. In addition, the temperature applied here was from 40 to 60 °C lower than those already reported in literature for acid-driven cellulose degradations. Phosphoric acid allowed both glucose and levulinic acid achievement. The latter is usually used to synthesize fuel additives, catalysts, solvents and herbicides, thereby enhancing the added value of the conversion of cellulose to glucose in phosphoric acid. Finally, 1H T1 NMR relaxometry showed its suitability to monitor cellulose degradation. The advantages of relaxomety are its quickness since only few minutes are needed to obtain relaxograms, and the possibility to use raw mixtures without the needing of sample preparation.

Rhizoglyphus robini Claparede, commonly known as the bulb mite, has been reported to complete its life-cycle utilizing filter paper as a sole dietary source. However, a complete cellulase complex necessary for crystalline cellulose degradation rarely occurs in arthropods. Experiments demonstrate that R. robini probably derives nutrients from the fungal mycelia growing on the filter paper rather than from the filter paper itself.

Formation of an activated cellulose (Cellulose) species $$CELLULOSE\xrightarrow[{air}]{{heat}}CELLULOSE*$$ is the designated first stage of cellulose degradation in air [1]. Little is known about either the process or the nature of CELLULOSE*. The transition, designatedT2, is observed as an exotherm around 300°C as the sample temperature is raised. No corresponding endotherm is observed on cooling. The process is therefore not reversible but is repeatable as subsequent reheating results in the exotherm being observed again. The exotherm is also found to be oxygen dependant. The effect of all the flame retardant treatments studied was to reduceT2 compared to the value for the untreated cotton.

Volatile aldehydes are produced during degradation of paper-based materials. This may result in their accumulation in archival and library repositories. However, no systematic study has been performed so far. In the frame of this study, passive sampling was carried out at ten locations in four libraries and archives. Despite the very variable sampling locations, no major differences were found, although air-filtered repositories were found to have lower concentrations while a non-ventilated newspaper repository exhibited the highest concentrations of volatile aldehydes (formaldehyde, acetaldehyde, furfural and hexanal). Five employees in one institution were also provided with personal passive samplers to investigate employees’ exposure to volatile aldehydes. All values were lower than the presently valid exposure limits. The concentration of volatile aldehydes, acetic acid, and volatile organic compounds (VOCs) in general was also compared with that of outdoor-generated pollutants. It was evident that inside the repository and particularly inside archival boxes, the concentration of VOCs and acetic acid was much higher than the concentration of outdoor-generated pollutants, which are otherwise more routinely studied in connection with heritage materials. This indicates that further work on the pro-degradative effect of VOCs on heritage materials is necessary and that monitoring of VOCs in heritage institutions should become more widespread.

The concentration of the hydroxyl radical generated during oxygen delignification was measured with a radical trapping agent. The N,N′-(5-nitro-1,3-phenylene)-bisglutaramide (NPG) was found to be effective but the experiments revealed that at pH higher than 11.5 the anionic form of hydroxyl radical – the oxyl anion radical – causes up to four times more chain cleavage than the hydroxyl radical. It was also found that the effect of both radicals in the pulp moderated at higher partial oxygen pressure and in the presence of hemicelluloses. The implications are that selectivity can be improved by maintaining a moderate alkaline pH profile, increasing the oxygen partial pressure, and retaining hemicelluloses in the brownstock.

Non-destructive methods of sampling during the physicochemical studies of historical objects such as old books and manuscripts seem to be an obvious choice. Since furfural has been shown to be one of the most abundant gaseous products of cellulose degradation, it can be considered as a convenient marker of degradation progress. The number of quantitative data concerning correlations between the emission of furfural and physicochemical and mechanical properties of paper is rather scarce in the literature. In the present studies, a model paper containing more than 99% of cellulose was aged inside closed vials at 90°C. Gaseous products of paper degradation were measured using sorption tubes filled with Tenax TA sorbent and GC-MS. The method has proved to be sufficiently sensitive for measuring furfural emission not only in accelerated degradation at 90°C but also during natural ageing of paper at room temperature even in relatively short time intervals of 2–28 days. The correlations between furfural emission and polymerization degree, pH, color, tear index, number of double folds and breaking length have been statistically confirmed at confidence level α=0.001. Basing on them it was possible to estimate the number of broken glycosidic bonds per one molecule of furfural formed during degradation—we found a value equal to 9.2.

This review reviews current research on the application of biotechnology to the bleaching of kraft pulp. Biobleaching research focuses on using white rot fungi, and ligninase and hemicellulase enzymes. Bleaching with white rot is generally very slow and the primary problems appear to be the control of cellulose degradation, the technical aspects of scale up and the avoidance of an initial lag phase. Ligninase enzymes depolymerize lignin and in combination with an extraction stage, partially bleach kraft pulp. Bleaching with hemicellulase enzymes looks promising. A reduced need for active chlorine has been obtained by boosting the bleachability of pulp through pretreatment with hemicellulose hydrolysing enzymes.

The effect of Phanerochaete chrysosporium cellobiose oxidase (CBO) on microcrystalline cellulose hydrolysis by Trichoderma cellulases was determined. Addition of 10 micrograms.ml-1 CBO to a reaction mixture containing T. viride cellulase increased glucose and cellobiose production by 10% and 48%, respectively. Cellulose weight loss was also enhanced by 19%. At higher concentrations (20-80 micrograms.ml-1), CBO decreased glucose and cellobiose production. Cellulose weight loss at 60 micrograms.ml-1 CBO was 76% compared to control cellulase reactions. This decrease appears to be due to inactivation of cellulase by H2O2 produced via CBO reaction, because addition of catalase enhances sugar production and cellulose weight loss. These findings suggest that at low, perhaps physiologically relevant concentrations, CBO enhances crystalline cellulose degradation by cellulases.

Bioelectrochemical systems (BESs) are emerging technologies which use microorganisms to catalyze the reactions at the anode and/or cathode. BES research is advancing rapidly, and a whole range of applications using different electron donors and acceptors has already been developed. In this mini review, we focus on technological aspects of the expanding application of BESs. We will analyze the anode and cathode half-reactions in terms of their standard and actual potential and report the overpotentials of these half-reactions by comparing the reported potentials with their theoretical potentials. When combining anodes with cathodes in a BES, new bottlenecks and opportunities arise. For application of BESs, it is crucial to lower the internal energy losses and increase productivity at the same time. Membranes are a crucial element to obtain high efficiencies and pure products but increase the internal resistance of BESs. The comparison between production of fuels and chemicals in BESs and in present production processes should gain more attention in future BES research. By making this comparison, it will become clear if the scope of BESs can and should be further developed into the field of biorefineries.

Financiadora de Estudos e Projetos The sugarcane weevil, Sphenophorus levis, is an important pest in sugarcane culture in São Paulo state, Brazil. To complete its life cycle, S. levis may depends on microorganisms that inhabit its intestinal tract and play an important key in the insect physiology and nutrition. In this study we report the characterization of the intestinal microbiota from population of insect larvae from field and laboratory. Analysis of 16S rDNA sequences revealed a total of fourteen genera, one group from Candidatus category and two uncultivable groups represented by Alfa-Proteobacteria, Beta-Proteobacteria, Gamma-Proteobacteria, Firmicutes and Bacteroidetes phylum. Microorganisms isolated through culture-dependent methods were classified according morphological parameters and using 16S rDNA molecular marker. In addition to bacteria, four filamentous fungi were isolated. It was observed a slightly higher bacterial diversity in field than in laboratory according to Shannon index (Field H'= 3,36; Laboratory H'= 3,26). It is also our objective in this work to search for microorganisms capable to degrade cellulose, an important event in the insect attack. From the cultivable microorganisms, five genera of bacteria and two filamentous fungi presented cellulolytic activity. This is the first study about S. levis microbiota which may contribute to understand the interaction plant-pathogen and also be useful for future development of new strategies for control of S. levis in sugarcane cultivation. A cana-de-açúcar é uma das mais importantes culturas no Brasil. No entanto, muitas pragas atacam esta cultura causando prejuízos econômicos. O gorgulho da cana-deaçúcar, Sphenophorus levis, é uma importante praga na cultura canavieira no Estado de São Paulo. Para completar o seu ciclo de vida, S. levis parece depender de microorganismos que habitam o seu trato intestinal e desempenham um importante função na fisiologia e nutrição do inseto. Neste estudo, nós realizamos a caracterização da microbiota intestinal de população de larvas de inseto campo e de laboratório. As análises das seqüências de 16S rDNA revelaram um total de catorze gêneros, um grupo da categoria Candidatus e dois grupos nãocultiváveis representados pelos filos Alfa-Proteobacteria, Beta-Proteobacteria, Gamma- Proteobacteria, Firmicutes e Bacteroidetes tanto em larvas do campo quanto nas do laboratório. Os microrganismos isolados através dos métodos dependentes de cultura foram agrupados de acordo com parâmetros morfológicos e através do marcador moléculas 16S rDNA. Além das bactérias também foram isolados quatro fungos filamentosos. Observou-se uma diversidade bacteriana levemente superior no campo do que no laboratório de acordo com o índice de Shannon (Campo H '= 3,36; Laboratório H' = 3,26). É também nosso objetivo neste trabalho encontrar microorganismos capazes de degradar celulose, um importante evento no ataque do inseto. Dos microorganismos cultiváveis, cinco gêneros de bactérias e dois fungos filamentosos apresentaram atividade celulolítica. Este é o primeiro estudo sobre a microbiota do S. levis que pode contribuir para a compreensão da interação planta-patógeno e também ser útil para o futuro desenvolvimento de novas estratégias de controle de S. levis no cultivo da cana-de-açúcar.

Cellulose is a linear polymer of glucose. The enzymatic degradation of cellulose can be stepwise or random depending on the enzymes acting on it. In this work, a stochastic approach is used to model stepwise degradation. The model predicts the distribution, mean and variance of the number or concentration of cellulose chains with j glucose units arising from hydrolysis at any time t . Estimates of the intensities (or reaction rate constants) of degradation are obtained by fitting the model to experimental data.

Atomic Force Microscopy was used on pure cotton cellulose paper to characterize the relationship between surface topographies and cellulose degradation patterns. Whatman N.1 chromatography paper and Fabriano Umbria paper artificially aged with different procedures and then naturally aged-were evaluated together with a sample from an original book. Evidence is found of a clear distinction between surface heights distribution of chiefly oxidised samples with respect to those where hydrolysis is the dominant process. In both cases, deteriorated paper shows surface features well different from the paper in good preservation state, in agreement to results from previous experiments. This is a first step that could open the way to AFM application as a qualitative diagnostic tool for library materials. The only way to achieve such a goal is to extend the experimentation to a wider population of paper samples, so to improve the statistical evaluation. Copyright © 2008 John Wiley & Sons, Ltd.

The kinetics of cellulose degradation was analysed by means of a two-stage model, characterised by an autoretardant and autocatalytic regime, later tempered by the consumption of glycosidic bonds in the amorphous regions. The proposed model explains the effects on the kinetic equations of different modes of ageing (acid hydrolysis, ageing in ventilated oven or sealed vessels), initial oxidation of cellulose and experimental procedures (with or without reduction of oxidised groups). The autoretardant branch can be analysed in a quantitative way, while the integration of the non-linear autocatalytic branch is allowed in some cases, characterised by the decrease of pH and/or emission of acid volatile organic compounds (VOCs). Most of the controversial results of the literature can be easily explained, but the proposed model offers also a guide for further studies on the kinetics of cellulose degradation.

Biomethanation of leaves of the legume L. leucocephala operated in batch reactors at different input volatile solids (12-18 g/L) proceeded in distinct metabolic phases. An initial cellulolytic phase of 4 d was followed by an early and active methanogenic phases (5-21 d) and a terminal phase of low-rate methanogenesis. Hydrolysis of cellulose was concentration-dependent and resulted in increased volatile acid levels. The trend of changes showed some variations at different input volatile solids. The changes in the levels of volatile acids followed an oscillatory pattern. The controlled rate of cellulose hydrolysis, levels of volatile acids, and steady-state levels of soluble carbohydrates and reducing sugars observed during active methanogenesis are indicative of interactive metabolic regulations. ? 1990 Humana Press Inc.

The introduction of an exogenous cellulolytic bacterium into a microbial community that was degrading rice straw effectively was evaluated. A stable coexistence of the indigenous and exogenous cellulolytic bacteria was achieved by adjusting the cultivation conditions. The obtained community required several subcultures to reach the highest degradation efficiency.

Plant residues, mainly made up of cellulose, are the largest fraction of organic carbon material in terrestrial ecosystems. Soil microorganisms are mainly responsible for the transfer of this carbon to the atmosphere, but their contribution is not accurately known. The aim of the present study was to identify bacterial populations that are actively involved in cellulose degradation, using the DNA-stable isotope probing (DNA-SIP) technique. (13)C-cellulose was produced by Acetobacter xylinus and incubated in soil for 7, 14, 30 and 90 days. Total DNA was extracted from the soil, the (13)C-labelled (heavy) and unlabelled (light) DNA fractions were separated by ultracentrifugation, and the structure of active bacterial communities was analysed by bacterial-automated ribosomal intergenic spacer analysis (B-ARISA) and characterized with denaturing gradient gel electrophoresis (DGGE). Cellulose degradation was associated with significant changes in bacterial community structure issued from heavy DNA, leading to the appearance of new bands and increase in relative intensities of other bands until day 30. The majority of bands decreased in relative intensity at day 90. Sequencing and phylogenetic analysis of 10 of these bands in DGGE profiles indicated that most sequences were closely related to sequences from organisms known for their ability to degrade cellulose or to uncultured soil bacteria.

The white-rot fungus Phanerochaete chrysosporium has two intracellular beta-glucosidases (BGL1A and BGL1B) belonging to glycoside hydrolase (GH) family 1. BGL1B effectively hydrolyzes cellobiose and cellobionolactone, but BGL1A does not. We have determined the crystal structure of BGL1A in substrate-free and gluconolactone complexed forms. The overall structure and the characteristic of subsite -1 (glycone site) were similar to those of other known GH1 enzymes. The loop regions covering on the (beta/alpha)(8) barrel was significantly deviated, and they form a unique subsite +1 (aglycone site) of BGL1A.

International audience; Carbon metabolism in anaerobic cellulolytic bacteria has been investigated essentially in Clostridium thermocellum, Clostridium cellulolyticum, Fibrobacter succinogenes, Ruminococcus flaVefaciens, and Ruminococcus albus. While cellulose depolymerization into soluble sugars by various cellulases is undoubtedly the first step in bacterial metabolisation of cellulose, it is not the only one to consider. Among anaerobic cellulolytic bacteria, C. cellulolyticum has been investigated metabolically the most in the past few years. Summarizing metabolic flux analyses in continuous culture using either cellobiose (a soluble cellodextrin resulting from cellulose hydrolysis) or cellulose (an insoluble biopolymer), this review aims to stress the importance of the insoluble nature of a carbon source on bacterial metabolism. Furthermore, some general and specific traits of anaerobic cellulolytic bacteria trends, namely, the importance and benefits of (i) cellodextrins with degree of polymerization higher than 2, (ii) intracellular phosphorolytic cleavage, (iii) glycogen cycling on cell bioenergetics, and (iv) carbon overflows in regulation of carbon metabolism, as well as detrimental effects of (i) soluble sugars and (ii) acidic environment on bacterial growth. Future directions for improving bacterial cellulose degradation are discussed.

Clostridia are anaerobic, endospore-forming prokaryotes that include strains of importance to human and animal health and physiology, cellulose degradation, solvent production and bioremediation. Their differentiation and related developmental programmes are not well understood at the molecular level. Recent genome sequencing and transcriptional-profiling studies have offered a glimpse of their inner workings and indicate that a better understanding of the orchestration of the molecular events that underlie their unique physiology, capabilities and diversity will pay major dividends.

Clostridium cellulolyticum ATCC 35319 has been extensively studied in the past few years on both the enzymatic and metabolic aspects of cellulose degradation and is considered as the model of mesophilic cellulolytic clostridia . As is true of most cellulolytic clostridia , this bacterium possesses an extracellular multi-enzymatic complex, the cellulosome. Cellulosomes are highly efficient in the degradation of plant cell wall polysaccharides. In C. cellulolyticum , most of the cellulosomal genes are localised in an approximately 26 kb DNA fragment, the cel cluster, where 12 genes have been identified to date cipC - cel48F - cel8C - cel9G - cel9E - orfX - cel9H - cel9J - man5K - cel9M - rgl11Y - cel5N . The C. cellulolyticum cellulosome is organised around the scaffolding protein CipC, which permits the binding of the different cellulosomal enzymes via interactions of dockerin–cohesin domains. Twelve cellulosomal enzymes have been identified including cellulases, hemicellulase and pectinase. The state of knowledge about the structure, ultrastructure, enzymatic activity, regulation and extracellular assembly of the C. cellulolyticum cellulosome are reviewed, and potential biotechnological exploitations discussed.