Clostridium thermocellum (C. thermocellum) is a standout thermophilic, spore-forming anaerobic bacterium renowned for its exceptional capacity to hydrolyze diverse substrates found in lignocellulosic biomass.
The identification of the cellulosome in C. thermocellum represents a groundbreaking achievement in microbiology, especially due to its effectiveness in degrading crystalline cellulose. These cellulosomes, some exceeding 2 MDa and forming larger supercomplexes known as polycellulosomes, are highly complex and integral to the organism’s degradative prowess.
The composition of cellulosomes in C. thermocellum adapts to the carbon source, showcasing versatile degradative capabilities encompassing various polysaccharides. Key scaffoldins, such as the prominent CipA, play a crucial role in the structural organization of cellulosomes. CipA’s cohesins (Type I) interacting with Type I dockerin and CBMIIIa, which binds crystalline cellulose, are particularly noteworthy.
The species-specific cohesin–dockerin interactions in C. thermocellum, governed by conserved sequences and structural intricacies, allow for continuous cellulosome reorganization, optimizing substrate targeting and binding. Anchoring proteins like SdbA, Orf2P, and OlpB contribute to cellulosome assembly and attachment to the cell surface, with Type I and Type II cohesins serving distinct roles.
The catalytic core of C. thermocellum’s cellulosome houses an array of enzymes adept at targeting cellulose, hemicellulose, and complex substrates. This diversity highlights the operational flexibility of the cellulosome and provides insights into evolutionary pathways for efficient energy conversion.
In essence, unraveling the structural and functional nuances of C. thermocellum’s cellulosomes offers valuable insights into the organism’s extraordinary ability to transform raw materials into usable energy, underscoring the intricate complexity of nature’s biochemical pathways.