Bacterial Cellulose Hydrolysis in Anaerobic Environmental Subsystems—Clostridium thermocellum and Clostridium stercorarium, Thermophilic Plant-fiber Degraders VLADIMIR V. ZVERLOV AND WOLFGANG H. SCHWARZ Department of Microbiology, Technische Universit¨ at M ¨ unchen, Freising, Germany Cellulose degradation is a rare trait in bacteria. However, the truly cellulolytic bacteria are ex- tremely efficient hydrolyzers of plant cell wall polysaccharides, especially those in thermophilic anaerobic ecosystems. Clostridium stercorarium, a thermophilic ubiquitous soil dweller, has a simple cellulose hydrolyzing enzyme system of only two cellulases. However, it seems to be better suited for the hydrolysis of a wide range of hemicelluloses. Clostridium thermocellum, an ubiquitous thermophilic gram-type positive bacterium, is one of the most successful cellu- lose degraders known. Its extracellular enzyme complex, the cellulosome, was prepared from C. thermocellum cultures grown on cellulose, cellobiose, barley β-1,3-1,4-glucan, or a mixture of xylan and cellulose. The single proteins were identified by peptide chromatography and MALDI- TOF-TOF. Eight cellulosomal proteins could be found in all eight preparations, 32 proteins occur in at least one preparation. A number of enzymatic components had not been identified previ- ously. The proportion of components changes if C. thermocellum is grown on different substrates. Mutants of C. thermocellum, devoid of scaffoldin CipA, that now allow new types of experiments with in vitro cellulosome reassembly and a role in cellulose hydrolysis are described. The charac- teristics of these mutants provide strong evidence of the positive effect of complex (cellulosome) formation on hydrolysis of crystalline cellulose. Key words: bacterial; cellulose; hydrolysis; anaerobic; thermophilic; cellulosome; mutant; scaf- foldin; enzyme; complex Introduction Climate is changing. One indication for this change is the large number of strong hurricanes in the United States in 2005, including Katrina and Rita, the hot summer in 2006, and the early and extremely dry spring in Europe in 2007. A long time indicator for global warming is the melting of the alpine glaciers, which can be observed by a larger number of people, in contrast to the less familiar melting of the Arctic and Antarctic ice shields and other indicators. 1 The Furtw¨ angler glacier on mount Kilimandjaro (Tansa- nia, Africa) has supposedly existed for 11,700 years but will disappear completely within 20 years. 1 The pub- lication of the Intergovernmental Panel on Climate Change (IPCC) report, 2 the first parts of which present the scientific evidence for global warming and the hu- Address for correspondence: Wolfgang H. Schwarz, Department of Microbiology, TUM, Am Hochanger 4, D-85350 Freising, Germany. +49- 8161-715445. wschwarz@wzw.tum.de man impact. The Stern report 3 made clear that im- mediate measures for the reduction of CO 2 emissions would be economically more efficient than subsequent repair measures and damage. With the growing prosperity of an increasing num- ber of people, associated with an advancing depen- dence on technology, the demand for energy is grow- ing steadily. More than 90% of our energy is currently made from stored natural resources that are rapidly de- pleted. The most important of those sources is crude (fossil) oil, which is burned with the release of CO 2 ,a climate-active greenhouse gas. This leads to a global increase in CO 2 content of the atmosphere. The re- duction of CO 2 release is a prime issue and calls the scientific world to present solutions for the produc- tion of sustainable energy. 4 New sustainably produced liquid and gaseous fuels for the energy sector could contribute considerably to a CO 2 -neutral energy us- age. Even more effective measures would be a more rational use of energy combined with energy saving. At present, only about 1% of the world’s energy need is met by biofuels. New biofuels are to be produced in Ann. N.Y. Acad. Sci. 1125: 298–307 (2008). C  2008 New York Academy of Sciences. doi: 10.1196/annals.1419.008 298