Chapter 2 - Cellulose as Potential Feedstock for Cellulase Enzyme Production: Versatility and Properties of Various Cellulosic Biomasses

Abstract

Cellulose is one of the most significant renewable energy sources present on earth and is also the most abundant biomolecule present in biomass. Hence producing indigenous cellulases for depolymerization of cellulose for use in various bioprocesses, namely biofuel production and commodity biochemical synthesis, is vital for the development of sustainable future biorefineries. Cellulolytic enzymes are a set of several enzymes, produced mainly by microorganisms both fungi and bacteria, that synergistically catalyze degradation of holocellulose-releasing oligosaccharides, cellobiose, and glucose units. Interestingly, cellulases are inducible enzymes, whose regulation is precisely regulated by activation and repression mechanisms. These inducible enzymes are produced only in the presence of complex cellulosic substrates, but repressed when simple sugars are present. The cellulosic substrates can either be pure substrates (cellulose powder) or raw lignocellulosic material. Lignocellulosic biomass, being plentiful as well as inexpensive, is usually the preferred substrate for the production of this enzyme system as compared to the pure substrates. Recent transcriptome profiling and quantitative proteomic approaches also reveal induction of specific proteins in the presence of utilizable lignocellulosic carbon sources by different microorganisms. This chapter discusses various pure and lignocellulosic substrates used for microbial cellulase production by either liquid submerged or solid-state fermentation.