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Title: Deletion of Caldicellulosiruptor bescii CelA reveals its crucial role in the deconstruction of lignocellulosic biomass

Background: Members of the bacterial genus Caldicellulosiruptor are the most thermophilic cellulolytic organisms described to date, and have the ability to grow on lignocellulosic biomass without conventional pretreatment. Different species vary in their abilities to degrade cellulose, and the presence of CelA, a bifunctional glycoside hydrolase that contains a Family 48 and a Family 9 catalytic domain, correlates well with cellulolytic ability in members of this genus. For example, C. hydrothermalis, which does not contain a CelA homolog, or a GH48 Family or GH9 Family glycoside hydrolase, is the least cellulolytic of the Caldicellulosiruptor species so far described. C. bescii, which contains CelA and expresses it constitutively, is among the most cellulolytic. In fact, CelA is the most abundant extracellular protein produced in C. bescii. The enzyme contains two catalytic units, a Family 9A-CBM3c processive endoglucanase and a Family 48 exoglucanase, joined by two Family 3b carbohydrate-binding domains. Although there are two non-reducing end-specific Family 9 and three reducing end-specific Family 48 glycoside hydrolases (producing primarily glucose and cellobiose; and cellobiose and cellotriose, respectively) in C. bescii, CelA is the only protein that combines both enzymatic activities. Results: A deletion of the celA gene resulted in a dramatic reduction inmore » the microorganism’s ability to grow on crystalline cellulose (Avicel) and diminished growth on lignocellulosic biomass. A comparison of the overall endoglucanase and exoglucanase activities of the mutant compared with the wild-type suggests that the loss of the endoglucanase activity provided by the GH9 family domain is perhaps compensated for by other enzymes produced by the cell. In contrast, it appears that no other enzymes in the C. bescii secretome can compensate for the loss of exoglucanase activity. The change in enzymatic activity in the celA mutant resulted in a 15-fold decrease in sugar release on Avicel compared with the parent and wild-type strains. In conclusion: The exoglucanase activity of the GH48 domain of CelA plays a major role in biomass degradation within the suite of C. bescii biomass-degrading enzymes.« less
Authors:
 [1] ;  [1] ;  [2] ;  [3] ;  [1]
  1. Univ. of Georgia, Athens, GA (United States). Department of Genetics; Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). BioEnergy Science Center
  2. National Renewable Energy Lab. (NREL), Golden, CO (United States). Biosciences Center; Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). BioEnergy Science Center
  3. National Renewable Energy Lab. (NREL), Golden, CO (United States). Biosciences Center; Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). BioEnergy Science Center
Publication Date:
OSTI Identifier:
1163406
Report Number(s):
NREL/JA-2700-63134
Journal ID: ISSN 1754-6834
Grant/Contract Number:
AC36-08GO28308
Type:
Accepted Manuscript
Journal Name:
Biotechnology for Biofuels
Additional Journal Information:
Journal Volume: 7; Journal Issue: 1; Journal ID: ISSN 1754-6834
Publisher:
BioMed Central
Research Org:
National Renewable Energy Laboratory (NREL), Golden, CO (United States); Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Country of Publication:
United States
Language:
English
Subject:
09 BIOMASS FUELS; 59 BASIC BIOLOGICAL SCIENCES; 37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY Chemical and Biosciences; Bioenergy; Cellulase; Thermophile