09/13/2010
New Method Allows Genetic Manipulation of Cellulose Degrading Clostridia
The Science
To be most useful for biofuel production, microbes need to have useful biochemical properties and be manipulable genetically. The cellulose degrading bacterium Clostridium thermocellum, while a promising candidate for consolidated bioprocessing approaches to biofuel production, has significant genetic manipulation challenges that have limited understanding of its mechanisms of biomass deconstruction. Researchers at DOE’s Bioenergy Science Center (BESC) now report a new method for genetic modification of C. thermocellum in the Proceedings of the National Academy of Sciences. Clostridium thermocellum is a thermophilic anaerobic bacterium that rapidly solubilizes cellulose with the aid of a multienzyme cellulosome complex. Creation of knockout mutants for Cel48S (also known as CelS, SS, and S8), the most abundant cellulosome subunit, was undertaken to gain insight into its role in enzymatic and microbial cellulose solubilization. Cultures of the Cel48S deletion mutant (S mutant) were able to completely solubilize 10 g/L crystalline cellulose.
Summary
This new method enabled the construction of a mutant lacking the gene for one of the organism’s major cellulase enzymes, Cel48S. The mutant depolymerizes crystalline cellulose 80% slower than the parent strain but, given sufficient time, it is still capable of complete cellulose degradation. This finding demonstrates that although Cel48S plays a major role in cellulose degradation, other less understood enzymes also contribute to this process and require further study. This result represents an important step forward in our ability to engineer this organism for bioenergy applications.
BER Program Manager
Dawn Adin
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Biological Systems Science Division
[email protected]
References
Olson, D. G., S. A Tripathi, R. J. Giannone, J. Lo, N. C. Caiazza, D. A. Hogsett, R. L. Hettick, A. M. Guss, G. Dubrovsky and L. R. Lynd. 2010. “Deletion of the Cel48S Cellulase from Clostridium thermocellum,” Proceedings of the National Academy of Sciences of the USA. doi/pnas.1003584107