To begin our search for new and diverse enzymes relevant to the deconstruction of the plant cell wall and conversion of their polysaccharides to soluble sugars, the best resource today is the CAZy database (http://www. cazy. org/). At this website, the various glycoside hydro­lases and related CAZymes (notably the carbohydrate esterases and the pectate lyases) are categorized into families and listed with appropriate information and links. Tens of thou­sands of enzymes are catalogued, and vital details, both general and specific, are very easily accessible.

Figure 5.4. Continuum for discovery and optimization of carbohydrate-active enzymes.

In view of the fact that many aerobic fungal and bacterial free enzyme systems comprise only a few (six to ten) major endo — and exo-glucanases and similarly restricted numbers of hemicellulases, carbohydrate esterases, and pectate lyases, it is somewhat surprising that we could or would want to examine more than the known CAZymes for their applicability in conversion processes. How much more diversity do we need over and above the enzymes listed in the CAZy database? Surely, the natural enzyme systems, particularly those from a given microbial species, are most coordinated among themselves and have “learned through evolution” to interact in an optimized manner to achieve maximum degradation of the plant cell wall polysaccharide substrates.

Nevertheless, Mother Nature’s needs are different from ours, and the natural ecosystems are not necessarily attuned to the requirements of our human desires and our industrial pro­cesses designed to achieve them. Consequently, there is a current trend toward discovery of new enzymes and improvement of known enzymes for the purpose of conversion of large amounts of cellulosic biomass to their simple sugar constituents.