Vesicle formation and cellulose degradation in Bacteroides succinogenes cultures: ultrastructural aspects

Gaudet, Geneviève; Gaillard, Brigitte

doi:10.1007/bf00425364

Cited by 26 publications

(17 citation statements)

References 7 publications

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“…For example, electron micrographs show that F. succinogenes clings very tightly to cellulose fibres, with erosion taking place right beneath the cells [183,185]. Indeed, many cellulolytic bacteria bind to cellulose, presumably by means of cellulases or of non-catalytic, cellulose-binding components present on the cell surface.…”

Section: Attachment Of Celhdolytic Or~anisms To the Substratementioning

confidence: 99%

The biological degradation of cellulose

Béguin

Aubert

1994

FEMS Microbiology Reviews

1,109

330

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Cellulolytic microorganisms play an important role in the biosphere by recycling cellulose, the most abundant carbohydrate produced by plants. Cellulose is a simple polymer, but it forms insoluble, crystalline microfibrils, which are highly resistant to enzymatic hydrolysis. All organisms known to degrade cellulose efficiently produce a battery of enzymes with different specificities, which act together in synergism. The study of cellulolytic enzymes at the molecular level has revealed some of the features that contribute to their activity. In spite of a considerable diversity, sequence comparisons show that the catalytic cores of cellulases belong to a restricted number of families. Within each family, available data suggest that the various enzymes share a common folding pattern, the same catalytic residues, and the same reaction mechanism, i.e. either single substitution with inversion of configuration or double substitution resulting in retention of the beta-configuration at the anomeric carbon. An increasing number of three-dimensional structures is becoming available for cellulases and xylanases belonging to different families, which will provide paradigms for molecular modeling of related enzymes. In addition to catalytic domains, many cellulolytic enzymes contain domains not involved in catalysis, but participating in substrate binding, multi-enzyme complex formation, or possibly attachment to the cell surface. Presumably, these domains assist in the degradation of crystalline cellulose by preventing the enzymes from being washed off from the surface of the substrate, by focusing hydrolysis on restricted areas in which the substrate is synergistically destabilized by multiple cutting events, and by facilitating recovery of the soluble degradation products by the cellulolytic organism. In most cellulolytic organisms, cellulase synthesis is repressed in the presence of easily metabolized, soluble carbon sources and induced in the presence of cellulose. Induction of cellulases appears to be effected by soluble products generated from cellulose by cellulolytic enzymes synthesized constitutively at a low level. These products are presumably converted into true inducers by transglycosylation reactions. Several applications of cellulases or hemicellulases are being developed for textile, food, and paper pulp processing. These applications are based on the modification of cellulose and hemicellulose by partial hydrolysis. Total hydrolysis of cellulose into glucose, which could be fermented into ethanol, isopropanol or butanol, is not yet economically feasible. However, the need to reduce emissions of greenhouse gases provides an added incentive for the development of processes generating fuels from cellulose, a major renewable carbon source.

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Section: Attachment Of Celhdolytic Or~anisms To the Substratementioning

confidence: 99%

The biological degradation of cellulose

Béguin

Aubert

1994

FEMS Microbiology Reviews

1,109

330

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“…Biochemical and ultrastructural studies have revealed glycogen storage in the cytoplasm of F. succinogenes, even in cells of young cultures (Stewart et al, 1981 ;Gaudet and Gaillard, 1987). This glycogen storage can represent as much as 70% of the total dry mass of the bacteria (Stewart et al, 1981).…”

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Futile cycling of glycogen in Fibrobacter succinogenes as shown by in situ¹H‐NMR and ¹³C‐NMR investigation

Gaudet

Forano²,

Dauphin

et al. 1992

European Journal of Biochemistry

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Glycogen was synthesized during all the growth phases in the rumen anaerobic cellulolytic bacterium Fibrobacter succinogenes. Glycogen synthesis and degradation were monitored using in situ 13C and 'H-NMR spectroscopy in resting cells of F. succinogenes. The cells were incubated at 37°C under anaerobic conditions with [l-13C]glucose and [2-'3C]glucose. 'H-NMR spectra were used to quantify enrichment by ' 3C of metabolism products. Glucose was utilized for energy requirements of the bacterium, essentially via the Embden-Meyerhof pathway, leading to the synthesis of succinate and acetate, while glycogen was stored. From [l-'3C]glucose, labeling occurred on C2 of succinate and acetate, and on both C1 and C6 of glycogen, the labeling on C1 being predominant. The C6-labeling of glycogen may be explained by scrambling and reversal of the glycolytic pathway at the triose-phosphate and fructose 1,6-bisphosphate level. When the bacteria were incubated first with [l-13C]glucose, then washed and incubated with [2-'3C]glucose, the pattern of 13C labeling in the products of the metabolism, as shown by 13C and 'H-NMR spectra, indicated that glycogen was degraded at the same time as it was being stored, suggesting futile cycling of glycogen. The hydrolysis of previously stored glycogen can provide, in the presence of glucose, up to 30% of the carbon source for the bacteria.

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“…*O0 The cellulosomes are readily visualized by scanning electron microscopy as discrete blebs on the cell Similar blebs have been observed on the surface of several ruminal cellulolytic bacteria that, like C. thermocellum, attach avidly to cellulose particles; this suggests that cellulosome-like structures may be important for the ruminal bacteria as well. 204, 205 One of the most prominent generalizations that can be made thus far is that exoglucanase enzymes are either less critical in the cellulolytic process in bacteria or have, at any rate, resisted isolation from the other enzymes of the cellulolytic complex. R. jlavefaciens and R .…”

Section: Bacterial Cellulasementioning

confidence: 99%

Cellulose Degradation by Ruminal Microorganisms

Weimer

1992

Critical Reviews in Biotechnology

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The rumen i s a highly developed digestive organ in which feed material, particularly plant fiber, is efficiently digested by a complex microbial fermentation. Cellulose, the major component of plant fiber, is digested in the rumen by an assemblage of anaerobic bacteria, fungi, and protozoa. While pure cellulose itself is completely digestible under the proper environmental conditions, the matrix interactions among structural biopolymers in natural plant material prevent the complete digestion of the cellulose component. Ruminal bacterial are probably the most active cellulose degraders in the rumen, but the fungi also play an important role, particularly in the physical disruption of recalcitrant tissue to render the cellulose more accessible to degradative enzymes. Cellulose degradation in the rumen is enhanced by attachment of microbial cells to the substrate and by synergistic interactions with noncellulolytic microbes, but is inhibited by factors that produce a low ruminal pH. Recent advances in continuous culture techniques and in the molecular biology of cellulase enzymes have permitted a better understanding of the cellulolytic process. Enhancement of ruminal cellulose fermentation will be best achieved in the near term by exploitation of recent improvements in the technology of substrate pretreatment. However, advances in the development of improved rumen microbial strains and more digestible forage varieties may yield additional improvements in ruminant cellulose utilization.

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Vesicle formation and cellulose degradation in Bacteroides succinogenes cultures: ultrastructural aspects

Cited by 26 publications

References 7 publications

The biological degradation of cellulose

The biological degradation of cellulose

Futile cycling of glycogen in Fibrobacter succinogenes as shown by in situ¹H‐NMR and ¹³C‐NMR investigation

Cellulose Degradation by Ruminal Microorganisms

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Vesicle formation and cellulose degradation in Bacteroides succinogenes cultures: ultrastructural aspects

Cited by 26 publications

References 7 publications

The biological degradation of cellulose

The biological degradation of cellulose

Futile cycling of glycogen in Fibrobacter succinogenes as shown by in situ1H‐NMR and 13C‐NMR investigation

Cellulose Degradation by Ruminal Microorganisms

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Futile cycling of glycogen in Fibrobacter succinogenes as shown by in situ¹H‐NMR and ¹³C‐NMR investigation