Cellulolytic and hemicellulolytic capacity of Acetivibrio clariflavus

Lignocellulosic biomass represents the largest available renewable source of carbon. It is a recalcitrant mixture of different polysaccharides and lignin. For its complete degradation, a large set of enzymes capable of cleaving its individual components is required. Several anaerobic bacteria produce high-molecular-weight multienzyme complexes called cellulosomes where the enzymes work in synergy for efficient degradation of the complex plant material. One of the anaerobic thermophilic cellulosome-forming bacteria is Acetivibrio clariflavus. Acetivibrio clariflavus was found to be one of the most abundant lignocellulose-solubilizing bacteria in various plant decaying environments. It produces sophisticated cellulosomal complex that is most similar to mesophilic Acetivibrio cellulolyticus cellulosome. In comparison with other anaerobic cellulosome-forming bacteria A. cellulolyticus and Acetivibrio thermocellus, A. clariflavus possesses lower number of cellulolytic enzymes. However, it is significantly better equipped for a degradation of hemicellulose, particularly xylan. Some strains, e.g., 4 - 2a, were also shown to utilize xylose. Efficient saccharification of plant biomass makes A. clariflavus a promising candidate for various biotechnological applications including biofuel production. KEY POINTS: • Acetivibrio clariflavus is anaerobic thermophilic cellulosome-forming bacterium. • Its cellulosomes target mostly cellulose and hemicellulose, in particular xylan. • The strains share most of xylanolytic enzymes but differ in xylose utilization.