Dataset Information

Cellulosomics of the cellulolytic thermophile Clostridium clariflavum.

ABSTRACT:

Background

Clostridium clariflavum is an anaerobic, thermophilic, Gram-positive bacterium, capable of growth on crystalline cellulose as a single carbon source. The genome of C. clariflavum has been sequenced to completion, and numerous cellulosomal genes were identified, including putative scaffoldin and enzyme subunits.

Results

Bioinformatic analysis of the C. clariflavum genome revealed 49 cohesin modules distributed on 13 different scaffoldins and 79 dockerin-containing proteins, suggesting an abundance of putative cellulosome assemblies. The 13-scaffoldin system of C. clariflavum is highly reminiscent of the proposed cellulosome system of Acetivibrio cellulolyticus. Analysis of the C. clariflavum type I dockerin sequences indicated a very high level of conservation, wherein the putative recognition residues are remarkably similar to those of A. cellulolyticus. The numerous interactions among the cellulosomal components were elucidated using a standardized affinity ELISA-based fusion-protein system. The results revealed a rather simplistic recognition pattern of cohesin-dockerin interaction, whereby the type I and type II cohesins generally recognized the dockerins of the same type. The anticipated exception to this rule was the type I dockerin of the ScaB adaptor scaffoldin which bound selectively to the type I cohesins of ScaC and ScaJ.

Conclusions

The findings reveal an intricate picture of predicted cellulosome assemblies in C. clariflavum. The network of cohesin-dockerin pairs provides a thermophilic alternative to those of C. thermocellum and a basis for subsequent utilization of the C. clariflavum cellulosomal system for biotechnological application.

SUBMITTER: Artzi L

PROVIDER: S-EPMC4582956 | biostudies-literature | 2014

REPOSITORIES: biostudies-literature

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Publications

Cellulosomics of the cellulolytic thermophile Clostridium clariflavum.

Artzi Lior L Dassa Bareket B Borovok Ilya I Shamshoum Melina M Lamed Raphael R Bayer Edward A EA

Biotechnology for biofuels 20140701

<h4>Background</h4>Clostridium clariflavum is an anaerobic, thermophilic, Gram-positive bacterium, capable of growth on crystalline cellulose as a single carbon source. The genome of C. clariflavum has been sequenced to completion, and numerous cellulosomal genes were identified, including putative scaffoldin and enzyme subunits.<h4>Results</h4>Bioinformatic analysis of the C. clariflavum genome revealed 49 cohesin modules distributed on 13 different scaffoldins and 79 dockerin-containing protei ...[more]

PMID: 26413154

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Project description:UnlabelledClostridium clariflavum is an anaerobic, cellulosome-forming thermophile, containing in its genome genes for a large number of cellulosomal enzyme and a complex scaffoldin system. Previously, we described the major cohesin-dockerin interactions of the cellulosome components, and on this basis a model of diverse cellulosome assemblies was derived. In this work, we cultivated C. clariflavum on cellobiose-, microcrystalline cellulose-, and switchgrass-containing media and isolated cell-free cellulosome complexes from each culture. Gel filtration separation of the cellulosome samples revealed two major fractions, which were analyzed by label-free liquid chromatography-tandem mass spectrometry (LC-MS/MS) in order to identify the key players of the cellulosome assemblies therein. From the 13 scaffoldins present in the C. clariflavum genome, 11 were identified, and a variety of enzymes from different glycoside hydrolase and carbohydrate esterase families were identified, including the glycoside hydrolase families GH48, GH9, GH5, GH30, GH11, and GH10. The expression level of the cellulosomal proteins varied as a function of the carbon source used for cultivation of the bacterium. In addition, the catalytic activity of each cellulosome was examined on different cellulosic substrates, xylan and switchgrass. The cellulosome isolated from the microcrystalline cellulose-containing medium was the most active of all the cellulosomes that were tested. The results suggest that the expression of the cellulosome proteins is regulated by the type of substrate in the growth medium. Moreover, both cell-free and cell-bound cellulosome complexes were produced which together may degrade the substrate in a synergistic manner. These observations are compatible with our previously published model of cellulosome assemblies in this bacterium.ImportanceBecause the reservoir of unsustainable fossil fuels, such as coal, petroleum, and natural gas, is overutilized and continues to contribute to environmental pollution and CO2 emission, the need for appropriate alternative energy sources becomes more crucial. Bioethanol produced from dedicated crops and cellulosic waste can provide a partial answer, yet a cost-effective production method must be developed. The cellulosome system of the anaerobic thermophile C. clariflavum comprises a large number of cellulolytic and hemicellulolytic enzymes, which self-assemble in a number of different cellulosome architectures for enhanced cellulosic biomass degradation. Identification of the major cellulosomal components expressed during growth of the bacterium and their influence on its catalytic capabilities provide insight into the performance of the remarkable cellulosome of this intriguing bacterium. The findings, together with the thermophilic characteristics of the proteins, render C. clariflavum of great interest for future use in industrial cellulose conversion processes.

Project description:BackgroundMicrobial cellulose conversion by Clostridium thermocellum 27405 occurs predominantly through the activity of substrate-adherent bacteria organized in thin, primarily single cell-layered biofilms. The importance of cellulosic surface exposure to microbial hydrolysis has received little attention despite its implied impact on conversion kinetics.ResultsWe showed the spatial heterogeneity of fiber distribution in pure cellulosic sheets, which made direct measurements of biofilm colonization and surface penetration impossible. Therefore, we utilized on-line measurements of carbon dioxide (CO2) production in continuous-flow reactors, in conjunction with confocal imaging, to observe patterns of biofilm invasion and to indirectly estimate microbial accessibility to the substrate's surface and the resulting limitations on conversion kinetics. A strong positive correlation was found between cellulose consumption and CO2 production (R2?=?0.996) and between surface area and maximum biofilm activity (R2?=?0.981). We observed an initial biofilm development rate (0.46 h-1, 0.34 h-1 and 0.33 h-1) on Whatman sheets (#1, #598 and #3, respectively) that stabilized when the accessible surface was maximally colonized. The results suggest that cellulose conversion kinetics is initially subject to a microbial limitation period where the substrate is in excess, followed by a substrate limitation period where cellular mass, in the form of biofilms, is not limiting. Accessible surface area acts as an important determinant of the respective lengths of these two distinct periods. At end-point fermentation, all sheets were digested predominantly under substrate accessibility limitations (e.g., up to 81% of total CO2 production for Whatman #1). Integration of CO2 production rates over time showed Whatman #3 underwent the fastest conversion efficiency under microbial limitation, suggestive of best biofilm penetration, while Whatman #1 exhibited the least recalcitrance and the faster degradation during the substrate limitation period.ConclusionThe results showed that the specific biofilm development rate of cellulolytic bacteria such as C. thermocellum has a notable effect on overall reactor kinetics during the period of microbial limitation, when ca. 20% of cellulose conversion occurs. The study further demonstrated the utility of on-line CO2 measurements as a method to assess biofilm development and substrate digestibility pertaining to microbial solubilization of cellulose, which is relevant when considering feedstock pre-treatment options.

Dataset Information

Cellulosomics of the cellulolytic thermophile Clostridium clariflavum.

Background

Results

Conclusions

Publications

Cellulosomics of the cellulolytic thermophile Clostridium clariflavum.

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