title: Dramatic performance of Clostridium thermocellum explained by its wide range of cellulase modalities.
abstract: Clostridium thermocellum is the most efficient microorganism for solubilizing lignocellulosic biomass known to date. Its high cellulose digestion capability is attributed to efficient cellulases consisting of both a free-enzyme system and a tethered cellulosomal system wherein carbohydrate active enzymes (CAZymes) are organized by primary and secondary scaffoldin proteins to generate large protein complexes attached to the bacterial cell wall. This study demonstrates that C. thermocellum also uses a type of cellulosomal system not bound to the bacterial cell wall, called the "cell-free" cellulosomal system. The cell-free cellulosome complex can be seen as a "long range cellulosome" because it can diffuse away from the cell and degrade polysaccharide substrates remotely from the bacterial cell. The contribution of these two types of cellulosomal systems in C. thermocellum was elucidated by characterization of mutants with different combinations of scaffoldin gene deletions. The primary scaffoldin, CipA, was found to play the most important role in cellulose degradation by C. thermocellum, whereas the secondary scaffoldins have less important roles. Additionally, the distinct and efficient mode of action of the C. thermocellum exoproteome, wherein the cellulosomes splay or divide biomass particles, changes when either the primary or secondary scaffolds are removed, showing that the intact wild-type cellulosomal system is necessary for this essential mode of action. This new transcriptional and proteomic evidence shows that a functional primary scaffoldin plays a more important role compared to secondary scaffoldins in the proper regulation of CAZyme genes, cellodextrin transport, and other cellular functions.
authors.affiliation: Biosciences Center, National Renewable Energy Laboratory, Golden, CO 80401, USA.; BioEnergy Science Center, Oak Ridge, TN 37831, USA.
authors.forename: Qi
authors.initials: Q
authors.lastname: Xu
authors.affiliation: BioEnergy Science Center, Oak Ridge, TN 37831, USA.; National Bioenergy Center, National Renewable Energy Laboratory, Golden, CO 80401, USA.
authors.forename: Michael G
authors.identifier: 0000-0002-8071-5764
authors.initials: MG
authors.lastname: Resch
authors.affiliation: Biosciences Center, National Renewable Energy Laboratory, Golden, CO 80401, USA.; BioEnergy Science Center, Oak Ridge, TN 37831, USA.
authors.forename: Kara
authors.identifier: 0000-0003-0915-1131
authors.initials: K
authors.lastname: Podkaminer
authors.affiliation: National Bioenergy Center, National Renewable Energy Laboratory, Golden, CO 80401, USA.
authors.forename: Shihui
authors.identifier: 0000-0002-9394-9148
authors.initials: S
authors.lastname: Yang
authors.affiliation: Biosciences Center, National Renewable Energy Laboratory, Golden, CO 80401, USA.; BioEnergy Science Center, Oak Ridge, TN 37831, USA.
authors.forename: John O
authors.initials: JO
authors.lastname: Baker
authors.affiliation: Biosciences Center, National Renewable Energy Laboratory, Golden, CO 80401, USA.; BioEnergy Science Center, Oak Ridge, TN 37831, USA.
authors.forename: Bryon S
authors.identifier: 0000-0002-2272-5059
authors.initials: BS
authors.lastname: Donohoe
authors.affiliation: BioEnergy Science Center, Oak Ridge, TN 37831, USA.; Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
authors.forename: Charlotte
authors.initials: C
authors.lastname: Wilson
authors.affiliation: BioEnergy Science Center, Oak Ridge, TN 37831, USA.; Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
authors.forename: Dawn M
authors.initials: DM
authors.lastname: Klingeman
authors.affiliation: BioEnergy Science Center, Oak Ridge, TN 37831, USA.; Thayer School of Engineering, Dartmouth College, Hanover, NH 03755, USA.
authors.forename: Daniel G
authors.identifier: 0000-0001-5393-6302
authors.initials: DG
authors.lastname: Olson
authors.affiliation: Biosciences Center, National Renewable Energy Laboratory, Golden, CO 80401, USA.; BioEnergy Science Center, Oak Ridge, TN 37831, USA.
authors.forename: Stephen R
authors.identifier: 0000-0001-7002-9034
authors.initials: SR
authors.lastname: Decker
authors.affiliation: BioEnergy Science Center, Oak Ridge, TN 37831, USA.; Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
authors.forename: Richard J
authors.identifier: 0000-0001-8551-0138
authors.initials: RJ
authors.lastname: Giannone
authors.affiliation: BioEnergy Science Center, Oak Ridge, TN 37831, USA.; Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
authors.forename: Robert L
authors.initials: RL
authors.lastname: Hettich
authors.affiliation: BioEnergy Science Center, Oak Ridge, TN 37831, USA.; Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
authors.forename: Steven D
authors.initials: SD
authors.lastname: Brown
authors.affiliation: BioEnergy Science Center, Oak Ridge, TN 37831, USA.; Thayer School of Engineering, Dartmouth College, Hanover, NH 03755, USA.
authors.forename: Lee R
authors.initials: LR
authors.lastname: Lynd
authors.affiliation: The Weizmann Institute of Science, Rehovot 7610001, Israel.
authors.forename: Edward A
authors.initials: EA
authors.lastname: Bayer
authors.affiliation: Biosciences Center, National Renewable Energy Laboratory, Golden, CO 80401, USA.; BioEnergy Science Center, Oak Ridge, TN 37831, USA.
authors.forename: Michael E
authors.initials: ME
authors.lastname: Himmel
authors.affiliation: Biosciences Center, National Renewable Energy Laboratory, Golden, CO 80401, USA.; BioEnergy Science Center, Oak Ridge, TN 37831, USA.
authors.forename: Yannick J
authors.initials: YJ
authors.lastname: Bomble
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D018533:Biomass; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D002480:Cellulase / Q000235:genetics / Q000378:metabolism*; D044603:Cellulosomes / Q000201:enzymology / Q000648:ultrastructure; D048013:Acetivibrio thermocellus / Q000201:enzymology* / Q000235:genetics / Q000648:ultrastructure; D017353:Gene Deletion; D005798:Genes, Bacterial; D046529:Microscopy, Electron, Transmission; D008954:Models, Biological; D020543:Proteome / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D020543:Proteome; C074074:cellulose binding protein A, Clostridium cellulovorans; D002480:Cellulase
keywords: Cell biology; biofuels; biomass; cellulases; cellulosomes