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Journal of Bacteriology, January 2009, p. 203-209, Vol. 191, No. 1
0021-9193/09/$08.00+0     doi:10.1128/JB.01190-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Cellodextrin and Laminaribiose ABC Transporters in Clostridium thermocellum{triangledown}

Yakir Nataf,1 Sima Yaron,1 Frank Stahl,2 Raphael Lamed,3 Edward A. Bayer,4 Thomas-Helmut Scheper,2 Abraham L. Sonenshein,5 and Yuval Shoham1*

Department of Biotechnology and Food Engineering, Technion-Israel Institute of Technology, Haifa, Israel,1 Institut für Technische Chemie, University of Hannover, Hannover, Germany,2 Department of Molecular Microbiology and Biotechnology, Tel-Aviv University, Ramat Aviv, Israel,3 Department of Biological Chemistry, The Weizmann Institute of Science, Rehovot, Israel,4 Department of Molecular Biology and Microbiology, Tufts University, Boston, Massachusetts5

Received 25 August 2008/ Accepted 19 October 2008

Clostridium thermocellum is an anaerobic thermophilic bacterium that grows efficiently on cellulosic biomass. This bacterium produces and secretes a highly active multienzyme complex, the cellulosome, that mediates the cell attachment to and hydrolysis of the crystalline cellulosic substrate. C. thermocellum can efficiently utilize only β-1,3 and β-1,4 glucans and prefers long cellodextrins. Since the bacterium can also produce ethanol, it is considered an attractive candidate for a consolidated fermentation process in which cellulose hydrolysis and ethanol fermentation occur in a single process. In this study, we have identified and characterized five sugar ABC transporter systems in C. thermocellum. The putative transporters were identified by sequence homology of the putative solute-binding lipoprotein to known sugar-binding proteins. Each of these systems is transcribed from a gene cluster, which includes an extracellular solute-binding protein, one or two integral membrane proteins, and, in most cases, an ATP-binding protein. The genes of the five solute-binding proteins were cloned, fused to His tags, overexpressed, and purified, and their abilities to interact with different sugars was examined by isothermal titration calorimetry. Three of the sugar-binding lipoproteins (CbpB to -D) interacted with different lengths of cellodextrins (G2 to G5), with disassociation constants in the micromolar range. One protein, CbpA, binds only cellotriose (G3), while another protein, Lbp (laminaribiose-binding protein) interacts with laminaribiose. The sugar specificity of the different binding lipoproteins is consistent with the observed substrate preference of C. thermocellum, in which cellodextrins (G3 to G5) are assimilated faster than cellobiose.

* Corresponding author. Mailing address: Department of Biotechnology and Food Engineering, Technion-Israel Institute of Technology, Haifa 32000, Israel. Phone: 972-4-8293072. Fax: 972-4-8293399. E-mail: yshoham{at}tx.technion.ac.il

{triangledown} Published ahead of print on 24 October 2008.

Journal of Bacteriology, January 2009, p. 203-209, Vol. 191, No. 1
0021-9193/09/$08.00+0     doi:10.1128/JB.01190-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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