ELUCIDATING THE ARCHITECTURAL ORGANIZATION AND DIVERSITY OF THE PSEUDOACTEROIDES CELLULOSOLVENS CELLULOSOME SYSTEM

Pseudobacteroides cellulosolvens is an anaerobic, mesophilic, cellulolytic bacterium capable of utilizing cellulose and cellobiose as a carbon source. Recently we have sequenced the B. cellulosolvens genome, and subsequent bioinformatic analysis revealed an incredible number of cellulosome-related components, including 75 cohesin modules scattered among 28 scaffoldins and more than 200 dockerin-bearing ORFs. In terms of numbers, this potentially represents the most intricate, compositionally diverse cellulosome system yet known in nature. Surprisingly, in comparison to previously described cellulosome systems, the apparent roles of the P. cellulosolvens cohesins are reversed, in that the type II cohesins are located on the enzyme-binding primary scaffoldin, whereas the type I cohesins are located on the anchoring scaffoldin. Such an organization seems to be unique to P. cellulosolvens. In addition, the dockerin-bearing ORFs include dozens of X60 modules which are known to stabilize type II cohesin-dockerin interactions. We focused on revealing the architecture of the cellulosomal structure by examining numerous interactions between cohesin and dockerin modules. Our results demonstrated the architectural organization and sequence diversity of the P. cellulosolvens cellulosomal components and thus provide the molecular basis for future understanding of the potential for a wide array of cohesin-dockerin specificities. Deep understanding of the interactions among cellulosomal components will enable us to design high-efficiency cellulosomes for conversion of plant-derived cellulosic biomass and improved production of biofuels.