BESC researchers identify key proteins in species of extremely thermophilic bacteria for breakdown of biomass into fermentable sugars
|The extremely thermophilic, cellulose-degrading Caldicellulosiruptor bescii. Source: ORNL. Click to enlarge.|
A team of researchers at the Department of Energy’s BioEnergy Science Center from North Carolina State University, Oak Ridge National Laboratory and the University of Georgia have analyzed the genomes of eight species of extremely thermophilic bacteria from the genus Caldicellulosiruptor and identified key proteins for the deconstruction of plant biomass into fermentable sugars. Team members had published the complete genome of five Caldicellulosiruptor species early in January; three had been reported previously.
The genus Caldicellulosiruptor, found in globally diverse sites from New Zealand to Iceland to Russia, contains the most thermophilic (optimal growth temperatures range from 70–78 °C, or 158–172 °F), plant biomass-degrading bacteria isolated to date. The analysis could aid in the production of next-generation biofuels.
Earlier, we had found that not all members of this group were able to equally degrade cellulose as others were. The main aim of this project was to figure what the true determinants were for strongly cellulolytic bacteria from this genus—what made them cellulolytic versus the others.—NCSU’s Sara Blumer-Schuette
By comparing the genomes of eight related yet variable species, the research team pinpointed which genes were unique to species with the ability to break down cellulose. The researchers, whose results are published in the Journal of Bacteriology, conducted additional analysis using proteomics to verify how these particular genes are expressed into proteins that perform cellulose degradation.
The team’s research uncovered a previously uncharacterized group of proteins determined to be adhesins, which help the bacteria grab onto a chunk of plant material to more efficiently break it apart.
Differentiating the strongly cellulolytic Caldicellulosiruptor species from the others is a specific genomic locus that encodes multi-domain cellulases from GH [glycoside hydrolases] families 9 and 48, associated with cellulose binding modules. This locus also encodes a novel adhesin associated with type IV pili, which was identified in the exo-proteome bound to crystalline cellulose.—Blumer-Schuette et al. (2012B)
Previously, we knew these bacteria would secrete enzymes that would then freely diffuse into their environment. We assumed that the enzymes would by chance stick to either cellulose or a piece of biomass in their environment and start to degrade it. Now we’re seeing that a lot of proteins are involved in maintaining a tight interface between the bacterium and cellulose.—Sara Blumer-Schuette
A key challenge in making the production of lignocellulosic biofuels cost-effective is improving the efficiency of access to the sugars in a plant‘s cell wall.
If we can understand the processes already in place with cellulose-degrading organisms such as the Caldicellulosiruptor microbes described here, we can make huge leaps in learning how to harness microbes to digest plant biomass and ferment sugars into biofuels at the same time.—Paul Gilna, director of BESC
Coauthors of the article include NCSU’s Sara Blumer-Schuette, Jeffrey Zurawski, Inci Ozdemir and Robert Kelly; ORNL’s Richard Giannone, Scott Hamilton-Brehm, James Elkins, Frank Larimer, Miriam Land, Loren Hauser, Robert Cottingham and Robert Hettich; and UGA’s Qin Ma, Yanbin Yin, Ying Xu, Irina Kataeva, Farris Poole and Michael Adams.
BESC is one of three DOE Bioenergy Research Centers established by the DOE’s Office of Science in 2007. The centers support multidisciplinary, multi-institutional research teams pursuing the fundamental scientific breakthroughs needed to make production of cellulosic biofuels, or biofuels from nonfood plant fiber, cost-effective on a national scale. The three centers are coordinated at ORNL, Lawrence Berkeley National Laboratory and the University of Wisconsin-Madison in partnership with Michigan State University.
Sara E. Blumer-Schuette, Inci Ozdemir, Dhaval Mistry, Susan Lucas, Alla Lapidus, Jan-Fang Cheng, Lynne A. Goodwin, Samuel Pitluck, Miriam L. Land, Loren J. Hauser, Tanja Woyke, Natalia Mikhailova, Amrita Pati, Nikos C. Kyrpides, Natalia Ivanova, John C. Detter, Karen Walston-Davenport, Shunsheng Han, Michael W. W. Adams, and Robert M. Kelly (2012A) Complete Genome Sequences for the Anaerobic, Extremely Thermophilic Plant Biomass-Degrading Bacteria Caldicellulosiruptor hydrothermalis, Caldicellulosiruptor kristjanssonii, Caldicellulosiruptor kronotskyensis, Caldicellulosiruptor owensensis, and Caldicellulosiruptor lactoaceticus. J. Bacteriol. 193:1483-1484 doi: 10.1128/JB.01515-10
Sara E. Blumer-Schuette, Richard J. Giannone, Jeffrey V. Zurawski, Inci Ozdemir, Qin Ma, Yanbin Yin, Ying Xu, Irina Kataeva, Farris L. Poole II, Michael W. W. Adams, Scott D. Hamilton-Brehm, James G. Elkins, Frank W. Larimer, Miriam L. Land, Loren Hauser, Robert W. Cottingham, Robert L. Hettich, and Robert M. Kelly (2012B) Caldicellulosiruptor core and pan genomes reveal determinants for non-cellulosomal thermophilic deconstruction of plant biomass. J. Bacteriol. doi: 10.1128/JB.00266-12