6-05: Glycan accessibility in monocots and its impact on cell wall recalcitrance

Enhanced polysaccharide digestibility by enzymes after pretreatment is a consequence of the increased accessibility of these polysaccharides to cellulolytic enzymes.  This accessibility is influenced by a number of cell wall properties and in this work we investigate the impacts of alkaline pretreatments on select cell wall properties for promising bioenergy grasses, including corn stover, miscanthus, and switchgrass.  As a component of this, changes in the binding affinities of individual carbohydrate binding modules (CBMs) derived from Clostridium thermocellum as a function of pretreatment are investigated.  Specifically, accessibility of five major categories of cell wall glycans including cellulose, xyloglucans, b-glucan, pectins, and xylans are assessed using CBMs from families 3, 6, 11, 35, 42, respectively.  The changes of binding affinity of the five CBM families associated with pretreatment are related to a number of cell wall properties including lignin content and removal, ferulate content and removal, water retention value, and glucan enzymatic digestibility.  Additionally, “glycome profiling” is used to characterize the pretreatment-induced alterations in the walls of these grasses in terms of cell wall glycan extractability and abundance.  This is done by screening sequentially extracted polysaccharide against an extensive and diverse library of plant cell wall glycan-directed antibodiess.  Together these findings are synthesized to develop a more comprehensive picture of the properties contributing cell wall recalcitrance in grasses.