Clostridium clariflavum is an anaerobic, thermophilic, Gram-positive bacterium that is capable of growth on crystalline cellulose as an exclusive source of carbon and energy. The genome of C. clariflavum has been sequenced to completion, and numerous cellulosomal genes were identified, including putative scaffoldin and enzyme subunits. Bioinformatic analysis of its genome revealed 49 cohesin modules distributed in 13 different scaffoldins and 79 dockerin-containing proteins, suggesting an abundance of putative cellulosome assemblies. The 13-scaffoldin system of C. clariflavum is highly reminiscent of the proposed 16-scaffoldin cellulosome system of Acetivibrio cellulolyticus. Analysis of the C. clariflavum type-I dockerin sequences indicated a very high level of conservation, wherein the putative recognition residues are remarkably similar to those of A. cellulolyticus. The numerous interactions among the cellulosomal components were elucidated using a standardized affinity-based ELISA fusion-protein system. The results revealed a rather simplistic recognition pattern of cohesin-dockerin interaction, whereby the type-I and type-II cohesins generally recognized the dockerins of the same type. The anticipated exception to this rule was the type-I dockerin of the ScaB adaptor scaffoldin which bound selectively to the type-I cohesins of ScaC and ScaJ. The findings present an intricate picture of predicted cellulosome assemblies of C. clariflavum and provide a basis for future utilization of the C. clariflavum cellulosomal system for biotechnological application.
