Accelerating hydrolysis of cellulose and xylan to monosugars by using hydrolyzing enzymes

Abstract

Cellulose and xylan are the most abundant renewable biomass in nature. However, they cannot be used directly as carbon sources for bacteria or yeast during fermentation to produce biofuel. To utilize cellulose and xylan, they need to be hydrolyzed to produce glucose and xylose. Nowadays, it is preferable to hydrolyze cellulose or xylan through enzymatic process because of its mild reaction conditions. In the case of cellulose, we hydrolyze filter paper by using cellulase from Trichoderma reesei as our model system. By using HPLC, we find two main peaks which correspond to glucose and cellobiose. These results show that the main hydrolytical products are glucose and cellobiose, and no other glucose oligomers are produced. Interestingly, after 12 h of hydrolysis, only 38% of filter paper is converted to glucose while 14 % is accumulated as cellobiose. We also hydrolyze xylan by using xylanase (Thermomyces lanuginosus) as our model system. It is found that after 12 h, only 2% of xylan is converted to xylose and 8% of xylan is hydrolyzed to xylobiose. Accumulation of cellobiose and xylobiose has significant implication since they cannot be used by bacteria or yeast to produce biofuel. In addition, cellobiose and xylobiose can inhibit the enzymatic hydrolysis of cellulose and xylan. Therefore, it is important to avoid the accumulation of cellobiose and xylobiose during enzymatic hydrolysis. To further hydrolyze cellobiose and xylobiose, we add additional β-glucosidase (from Aspergillus niger) and β-xylosidase (from Selenomonas ruminantium) to cellulase and xylanase, respectively. Our results show that the amount of β-glucosidase and β-xylosidase can be optimized to maximize the concentrations of monosugars and accelerate the hydrolysis of cellulose and xylan.