Determination of the chemistry involved in enzymatic breakdown of crystalline cellulose

Abstract

Lignin, cellulose and hemicellulose, the key components of lignocellulosic biomass are closely associated with each other at the plant cell level. This close association, together with the partly crystalline nature of cellulose serves to protect cellulose in native biomass from enzymatic hydrolysis. The predominant polysaccharide in most plant cell walls is cellulose, which forms long liner fibrils of approximately 30-40 hydrogen-bonded chains of β-(1,4) glucopyranosides that have a native degree of polymerization (DP) of ~2,000-15,000 depending the starting bioresource (O’Sullivan, 1997). Cellulose can exhibit several different supra-molecular structures, including amorphous, para-crystalline and crystalline. Native cellulose has been shown to be composed of two different crystalline forms in addition to para-crystalline and amorphous (Attala, et al., 1984). In general, the bioavailability of cellulose is controlled by a variety of factors including the degree of cellulose crystallinity, lignin content and structure, acetylated hemicelluloses and lignin-carbohydrate complexes (Clark, A.J., 1997).

The deconstruction of cellulose to glucose has become a key technological challenge for green biofuel production. Researchers are searching for novel cellulolytic enzymatic properties in many organisms including termites, sea worms, and the gut section of several mammalians (Baker, J.O., et al., 1998; Mansfield, S.D., et al., 2003; McCarter, S.L., et al., 2002; Wyman, C.E., 2005). The crystalline regions of cellulose are normally considered to be more difficult to degrade than amorphous domains due to chains tightly-held by intermolecular hydrogen bonding. Several researchers demonstrated increased crystallinity during enzymatic hydrolysis, and concluded that the loosely structured amorphous regions were hydrolyzed more rapid than the crystalline domains (Cao, Y., et al., 2002; Cao, Y., et al. 2004). The intestinal Fortitude Fibro-biotic program did find two bacterial isolates that had a unique enzyme activity on cellulose resulting in treated cellulose samples having a decrease in crystallinity. This type of enzymatic activity has not been previously reported or isolated for biofuel production. Two bacterial isolates (SDCC 1b and SDCC 2a) have had their genomes sequenced and are in the process of genome annotation.

This research program was directed at determining how cellulosic ultrastructure changes when fermented with these novel mammalian bacterial isolated as a function of time and multiply bioresources. In addition, the ability of related pig fecal bacteria to degrade and modify the structure of cellulosic biomass were determined. These results will help determine how effective the fermentation of cellulose with SDCC 1b/2a and pig fecal bacterial is on the reactivity and ultrastructure of cellulose.