Abstract <p>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 <i>Acetivibrio clariflavus</i>. <i>Acetivibrio clariflavus</i> 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 <i>Acetivibrio cellulolyticus</i> cellulosome. In comparison with other anaerobic cellulosome-forming bacteria <i>A</i>. <i>cellulolyticus</i> and <i>Acetivibrio thermocellus</i>, <i>A. clariflavus</i> 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 <i>A. clariflavus</i> a promising candidate for various biotechnological applications including biofuel production.</p> Key points <p><i>• Acetivibrio clariflavus is anaerobic thermophilic cellulosome–forming bacterium.</i></p> <p><i>• Its cellulosomes target mostly cellulose and hemicellulose, in particular xylan.</i></p> <p><i>• The strains share most of xylanolytic enzymes but differ in xylose utilization.</i></p>