Journal
INCREDIBLE ANAEROBES: FROM PHYSIOLOGY TO GENOMICS TO FUELS
Volume 1125, Issue -, Pages 298-307Publisher
BLACKWELL PUBLISHING
DOI: 10.1196/annals.1419.008
Keywords
bacterial; cellulose; hydrolysis; anaerobic; thermophilic; cellulosome; mutant; scaffoldin; enzyme; complex
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Cellulose degradation is a rare trait in bacteria. However, the truly cellulolytic bacteria are extremely 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 cellulose degraders known. Its extracellular enzyme complex, the cellulosome, was prepared from C thermocellum cultures grown on cellulose, cellobiose, barley beta-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 previously. 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 characteristics of these mutants provide strong evidence of the positive effect of complex (cellulosome) formation on hydrolysis of crystalline cellulose.
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