The diversity of cellulosomal structural proteins is very similar to what is found in Clostridium thermocellum and other cellulosomal microorganisms. However, chronic myelocytic leukemia CBM2 modules are not very common in cellulolytic clostridia, with C. phytofermentans and C. cellulovorans each having one such domain. C. clariflavum has four of these domains and they are associated with three separate multi-cohesin (Type I) domains with no anchoring mechanism. It may also be noted that the organization of the scaffoldin and anchoring proteins resembles the cellulosomal complexes found in the mesophile Acetivibrio cellulolyticus [42,43] more than it does the C. thermocellum cellulosome. Pyruvate metabolism The genome sequence of C. clariflavum revealed that this organism possesses a standard glycolytic pathway.

However, the pyruvate node is slightly different from other Cluster III clostridia in that C. clariflavum possesses genes for both pyruvate kinase (Clocl_1090) and pyruvate dikinase (PPDK, Clocl_2755). This may be of relevance to pyruvate metabolism because genomes of cellulolytic clostridia from cluster III reveal that the pathway from phosphoenol pyruvate (PEP) to pyruvate in these organisms uses either PPDK (Clostridium thermocellum ATCC 27405 and DSM 1313) or pyruvate kinase (C. cellulolyticum, C. papyrosolvens). There are nevertheless cellulolytic clostridia outside of Cluster III that also possess both, as is the case of Clostridium cellulovorans. Hemicellulose sugars metabolism C. clariflavum possesses a variety of xylanolytic enzymes that allow it to break down xylan completely to xylose, unlike C.

thermocellum, which is only able to break xylan down to xylooligomers. One of the key enzymes in xylose utilization, xylose isomerase, is found in mesophilic xylanolytic/cellulolytic clostridia such as C. cellulolyticum, C. phytofermentans, C. papyrosolvens and C. cellulovorans, as well as in hyperthermophiles like Caldicellulosiruptor bescii. However, the genome of C. clariflavum does not seem to possess a xylose isomerase. On the other hand, a putative xylulose kinase has been identified in C. clariflavum (Clocl_2440), which is a key difference from C. thermocellum, where this enzyme is absent. Xylulose kinase is usually adjacent to or in the same operon as xylose isomerase. A xylose epimerase (5.1.3.

4) that leads to the production of L-ribulose-5P is immediately adjacent (Clocl_2439) to the putative xylulose kinase. In C. clariflavum, these genes are also surrounded by a variety of hemicellulose-active enzymes in an operon from Clocl_2435 to Clocl_2447, that includes 3 family Carfilzomib 10 glycosyl hydrolases. Considering that none of these enzymes is present in C. thermocellum, there should be great interest in further exploring this operon in C. clariflavum and in environmental isolates. An alternative xylose epimerase (5.1.3.