The Genus Prevotella, A Resource of Enzymes for Hemicellulose Degradation

Abstract

Hemicellulose and cellulose constitute two major targets in plants for cellulosic ethanol production. Whereas cellulose is a highly homogenous polymer of glucose joined in beta-1,4-glycosidic linkages, hemicellulose is mostly a heterogenous polymer of xylose and arabinose. Thus, the common arrangement of sugars in hemicelluloses, such as xylans from bioenergy feedstocks, is a beta-1,4-linked xylose backbone with side chains of arabinofuranosyl, acetyl, and 4-O-methyl glucuronyl groups. Complete hydrolysis of hemicellulose, therefore, requires a complex set of enzymes. Nature has selected for microorganisms that derive their carbon and energy sources from hemicellulose by an enzymatic action that deconstructs the polymer into its component sugars. Such microorganisms include the genus Prevotella. We are, therefore, using genomics, bioinformatics, biochemical, and structural analyses to unravel the strategies used by Prevotella spp to break down hemicellulose. Our ultimate goal is to rationally assemble enzyme cocktails from these microorganisms for use in the bioenergy industry. We have demonstrated that Prevotella bryantii grows rapidly on hemicellulose. Furthermore, the sequencing of its genome has allowed identification of genes likely to encode products for deconstruction of hemicellulosic substrates. Several of these genes have been expressed as recombinant proteins in E. coli. Experiments that aimed at examining the synergistic activities of the P. bryantii enzymes have led us to reconstitute an enzyme complex that degrades wheat arabinoxylan into its component sugars. This enzyme mixture is a promising product in our effort to deconstruct hemicellulose. We are currently using transcriptomic analyses to improve the enzyme cocktail, and structural analysis is also being applied to rationally synthesize new carbohydrate active enzymes with enhanced activities.