Cellobiose

Abstract: Cellulose is the main polymeric component of the plant cell wall, the most abundant polysaccharide on Earth, and an important renewable resource. Basidiomycetous fungi belong to its most potent degraders because many species grow on dead wood or litter, in environment rich in cellulose. Fungal cellulolytic systems differ from the complex cellulolytic systems of bacteria. For the degradation of cellulose, basidiomycetes utilize a set of hydrolytic enzymes typically composed of endoglucanase, cellobiohydrolase and β-glucosidase. In some species, the absence of cellobiohydrolase is substituted by the production of processive endoglucanases combining the properties of both of these enzymes. In addition, systems producing hydroxyl radicals based on cellobiose dehydrogenase, quinone redox cycling or glycopeptide-based Fenton reaction are involved in the degradation of several plant cell wall components, including cellulose. The complete cellulolytic complex used by a single fungal species is typically composed of more than one of the above mechanisms that contribute to the utilization of cellulose as a source of carbon or energy or degrade it to ensure fast substrate colonization. The efficiency and regulation of cellulose degradation differs among wood-rotting, litter-decomposing, mycorrhizal or plant pathogenic fungi and yeasts due to the different roles of cellulose degradation in the physiology and ecology of the individual groups.

Abstract: Decomposition experiments of microcrystalline cellulose were conducted in subcritical and supercritical water (25 MPa, 320−400 °C, and 0.05−10.0 s). At 400 °C hydrolysis products were mainly obtained, while in 320−350 °C water, aqueous decomposition products of glucose were the main products. Kinetic studies of cellulose, cellobiose, and glucose at these conditions showed that below 350 °C the cellulose decomposition rate was slower than the glucose and cellobiose decomposition rates, while above 350 °C, the cellulose hydrolysis rate drastically increased and became higher than the glucose and cellobiose decomposition rates. Direct observation of the cellulose reaction in high-temperature water at high-pressure conditions by using a diamond anvil cell (DAC) showed that, below 280 °C, cellulose particles became gradually smaller with increasing reaction time but, at high temperatures (300−320 °C), cellulose particles disappeared with increasing transparency and much more rapidly than expected from the lowe...

Abstract: In this paper we propose a new method to hydrolyze cellulose rapidly in supercritical water (SCW) to recover glucose, fructose and oligomers (cellobiose, cellotriose, cellotetraose, etc.). Cellulose decomposition experiments were conducted with a flow type reactor in the range of temperature from 290 to 400°C at 25 MPa. A high pressure slurry feeder was developed to feed the cellulose–water slurries. Hydrolysis product yields (around 75%) in supercritical water were much higher than those in subcritical water. At a low temperature region, the glucose or oligomer conversion rate was much faster than the hydrolysis rate of cellulose. Thus, even if the hydrolysis products, such as glucose or oligomers, are formed, their further decomposition rapidly takes place and thus high yields of hydrolysis products cannot be obtained. However, around the critical point, the hydrolysis rate jumps to more than an order of magnitude higher level and becomes faster than the glucose or oligomer decomposition rate. This is the reason why we obtained a high yield of hydrolysis products in supercritical water.

Abstract: The high cost of enzymes for saccharification of lignocellulosic biomass is a major barrier to the production of second generation biofuels. Using a combination of genetic and biochemical techniques, we report that filamentous fungi use oxidative enzymes to cleave glycosidic bonds in cellulose. Deletion of cdh-1, the gene encoding the major cellobiose dehydrogenase of Neurospora crassa, reduced cellulase activity substantially, and addition of purified cellobiose dehydrogenases from M. thermophila to the Δcdh-1 strain resulted in a 1.6- to 2.0-fold stimulation in cellulase activity. Addition of cellobiose dehydrogenase to a mixture of purified cellulases showed no stimulatory effect. We show that cellobiose dehydrogenase enhances cellulose degradation by coupling the oxidation of cellobiose to the reductive activation of copper-dependent polysaccharide monooxygenases (PMOs) that catalyze the insertion of oxygen into C–H bonds adjacent to the glycosidic linkage. Three of these PMOs were characterized and s...