Cellulosomics of the cellulolytic thermophile Clostridium clariflavum

Clostridium clariflavum is an anaerobic, thermophilic, Gram-positive bacterium, capable of growth on crystalline cellulose as a single carbon source. 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 the C. clariflavum genome revealed 49 cohesin modules distributed on 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 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 ELISA-based 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 reveal an intricate picture of predicted cellulosome assemblies in C. clariflavum. The network of cohesin-dockerin pairs provides a thermophilic alternative to those of C. thermocellum and a basis for subsequent utilization of the C. clariflavum cellulosomal system for biotechnological application.