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BioMed Research International
Volume 2015 (2015), Article ID 304523, 11 pages
Research Article

Expression of Heterologous Cellulases in Thermotoga sp. Strain RQ2

Department of Biological Sciences, Bowling Green State University, Bowling Green, OH 43403, USA

Received 19 September 2014; Revised 21 January 2015; Accepted 6 February 2015

Academic Editor: George Tsiamis

Copyright © 2015 Hui Xu et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


The ability of Thermotoga spp. to degrade cellulose is limited due to a lack of exoglucanases. To address this deficiency, cellulase genes Csac_1076 (celA) and Csac_1078 (celB) from Caldicellulosiruptor saccharolyticus were cloned into T. sp. strain RQ2 for heterologous overexpression. Coding regions of Csac_1076 and Csac_1078 were fused to the signal peptide of TM1840 (amyA) and TM0070 (xynB), resulting in three chimeric enzymes, namely, TM1840-Csac_1078, TM0070-Csac_1078, and TM0070-Csac_1076, which were carried by Thermotoga-E. coli shuttle vectors pHX02, pHX04, and pHX07, respectively. All three recombinant enzymes were successfully expressed in E. coli DH5α and T. sp. strain RQ2, rendering the hosts with increased endo- and/or exoglucanase activities. In E. coli, the recombinant enzymes were mainly bound to the bacterial cells, whereas in T. sp. strain RQ2, about half of the enzyme activities were observed in the culture supernatants. However, the cellulase activities were lost in T. sp. strain RQ2 after three consecutive transfers. Nevertheless, this is the first time heterologous genes bigger than 1 kb (up to 5.3 kb in this study) have ever been expressed in Thermotoga, demonstrating the feasibility of using engineered Thermotoga spp. for efficient cellulose utilization.