Degradation of xylan by a new strain of thermophilic Clostridium.

摘要

Much current interest is focused on application of microorganisms to degrading plant polysaccharides, or biomass. Those degradative organisms which are anaerobes use fermentative processes to metabolize the mono- and disaccharides (sugars) produced during polysaccharide break-down. Energy-rich substances including alcohols, methane, and hydrogen may be produced from such fermentations.;Currently, no thermophilic organism is known which is able to both degrade the most abundant plant polysaccharides (cellulose and the hemicelluloses) and to ferment the sugars produced by such degradation. Hence much effort has focused on the simultaneous culturing (co-culturing) of organisms, so that more complete dissimilation of polysaccharides and more efficient fermentation of sugars may be effected.;The intent of our research has been the isolation of a thermophilic, polysaccharide-degrading anaerobe which could prove suitable for co-culturing with organisms such as Clostridium thermocellum, a prominent cellulose-degrading bacterium.;We have isolated such an organism from Kansas soil. Our isolate vigorously degrades xylan, a hemicellulose, as well as several starchy substrates and other polysaccharides, though not cellulose. In addition, the isolate ferments all common mono- and di-saccharide components of plant polysaccharides. Though its fermentation is largely acidic, it also produces significant amounts of ethanol and n-butanol. Biochemical and metabolic characterization of the isolate have allowed us to distinguish it from previously-reported strains of the genus Clostridium, though we currently have insufficient evidence to report it as a new species.;Some biomass-degrading microorganisms are thermophiles--i.e., they grow at unusually high temperatures. Under these conditions, the recovery and processing of fermentation end-products is markedly more efficient and less costly than at more moderate temperatures. Thus, thermophilic anaerobes hold most promise for the development of profitable biomass-degrading systems.;Initial studies of the isolate's xylan-degrading system reveal that the organism produces at least six separate xylanases when the isolate grows in media containing xylose, a component of xylan. In xylan medium, the isolate also produces a yellow, highly-charged substance which co-migrates electrophoretically with its active xylanase(s). This substance may be analogous to the yellow substrate affinity substance (YAS) produced by C. thermocellum in cellulose medium.