## 2 Metagenomic Discovery of New Microbial Cellulases  
Commercial cellulase products are already widely used in some traditional industrial applications such as food processing, the textile industry, detergent products, and pulp and paper industries [4; 25; 27; 45]. Enzyme companies Novozymes of Denmark and Monosanto of St. Louis in US have announced a joint global venture [46]; and aimed to increase crop yields while reducing inputs presumably by enhancing soil organic matter fertility via microbial enzyme products. More profound contemporary applications of new generations of highly efficient and capable cellulases in saccharification of raw and pretreated lignocellulosic substrates for commercial production of cellulosic ethanol and in supplementation as exogenous feed enzyme additives in enhancing feed energy and carbon conversion efficiency in agricultural food animal feed industries are the two key directions in developing a bioreinery-based bioeconomy in the continued global economic development [11; 25; 26; 47]. Novel and efficient cellulases as biocatalysts are the key driver for these new developments. Currently, commercial cellulase genes were obtained through the traditional cloning techniques from _Trichoderma_ and _Aspergillus_ fungal species and _Bacillus sp._ with further engineering for steadily improved enzyme functionality and protein yields and a dramatically reduced fermentation cost [4; 25; 48; 49]. Prospectively, a commer  
Figure 1: An illustration of the major processes and biological steps in utilization and conversion of agricultural waste feedstock biomass in providing sustainable functional foods and food animal production and renewable lignocellulosic ethanol, functional soluble fiber and other biomaterials with an emphasis on the essential roles of biomass-degrading enzymes as novel industrial enzymes. cial scale of cellulosic ethanol production was projected to launch businesses on multiple sites [50]. Needless to say, there is a continued need to further improve cellulase enzyme specific activities to ensure that this newly emerging cellulosic ethanol industry will become progressively viable and economically competitive [51]. On the other hand, there is still a lack of well recognized cellulase enzyme products due to limited enzyme activity in hydrolyzing natural raw lignocellulosic of feed sources for their effective applications in animal production [29; 30; 31; 32]. Under this context, the discovery and characterization of newly emerged novel cellulaases, as described herein, have been discussed for their potential commercial applications as novel and efficient cellulase products for both the cellulosic ethanol production and the animal feed enzyme industry, among others. One newly evolved possible approach for discovering new cellulases involves metagenomic mining, including metagenomic analysis and metagenomic expression library, for microbial cellulases in random samples of DNA fragments from material extracted directly from complex environments. This metagenomic approach circumvents the highly restrictive requirement that organisms be culturable [52]. This allows enzymes from a far richer variety of microorganisms to be sampled and characterized. For example, functional screening of microbial metagenomic expression libraries [44; 45] and gene-centric based metagenomic gene cataloguing have unearthed a diversity of cellulases from the bovine rumen [52; 53; 54; 55], the rabbit occum [56], the human gut [57], the rodent gut [58], hindgut of wood-feeding higher termites [59], the earthworm gut [60; 61], decaying wood [62], soil [63; 64; 65] and environmental samples [66]. By comparing to the major metagenomic database, [PERSON] et al. (2010) have concluded that animal gut metagenomes are substantially enriched with novel glycosyl hydrolases [67]. [PERSON] et al. (2019) identified a multifunctional processive endocellulose from the porcine hindgut microbiome [45].