## 7 Microbial Processive Cellulase Properties of Hydrolyzing Natural Crystalline Substrates
[45] had a specific activity (Table 1, 0.216 vs. 24.8 umol D-glucose/mg protein.min) in hydrolyzing the model insoluble crystalline cellulosic substrate Avicel. Specific cellulase activities are expressed and converted into the international unit (1 IU = umol D-glucose per mg pure enzyme protein per min) in some of the well characterized bacterial endocellulaes reported in the literature. The GH5-p4818 Cel5_2A endoglucanase activity on Avicel by [PERSON] et al. [45] was about 20-215 folds higher than the range of activities (0.0010-0.0105 umol D-glucose/mg protein.min) determined with filter paper for the six _Thermobifida fusca_ endoglucanas and exocellulaes [120]. The GH5-p4818 Cel5_2A endoglucanase activity on Avicel was about 8- to 19-fold higher than the activities (0.011 and 0.024 umol D-glucose/mg protein.min) determined with Sigmacell-20 for the termite saliva endogenous endoglucanase [128]. While the GH5-p4818 Cel5_2A endoglucanase activity on Avicel was about 30% higher than the activity (0.1696 umol D-glucose/mg protein.min) measured with Avicel for the _Clostridium cellululosomal GH9 progressive endoglucanase CelF [129], its activity was about 36- to 119-fold higher than the activities (0.0018-0.0059 umol D-glucose/mg protein.min) measured with Avicel for a total of 13 other _Clostridium cellululosomal GH9 endoglucanas [130]_. The GH5-p4818 Cel5_2A endoglucanase activity on Avicel was about 18% higher than the activity (0.1828 umol D-glucose/mg protein.min) determined with Avicel for the _Clostridium thermocellum_ noncellulosomal processive endoglucanase GH9B (Celf) [131], and was about 431-fold higher than the activity (0.0005 umol D-glucose/mg protein.min) measured with bacterial microcrystalline cellulose (BMCC) for the _Clostridium thermocellum_ cellulosomal non-processive endoglucanase GH9C (Cbha) [132]. The GH5-p4818 Cel5_2A endoglucanase activity on Avicel in this study was about 9- to 97-fold higher than the range of activities (0.0022-0.0218 umol D-glucose/mg protein.min) determined with Avicel for the three _Saccharomyces degradans_ GH5 processive endoglucanas of Cel5G, Cel5H and Cel5J [133]. GH5-p4818 Cel5_2A endoglucanase activity on Avicel by [PERSON] et al. [45] was three-fold lower than the activity (0.8187 umol D-glucose/mg protein.min) measured with Avicel (PH105) for the _Bacillus subtilis_ GH5 endoglucanase Bscel5 [75], however, the _Bacillus subtilis_ Bscel5 was a classic non-processive endoglucanase. The GH5-p4818_2A endoglucanase activity on Avicel in this study was about 24- and 71-fold higher than the activities (0.0030 and 0.0088 umol D-glucose/mg protein.min) measured with Avicel for novel GH5 endoglucanas obtained from vermicompost and sugarcane soil metagenomes [61,134]. Thus, this truncated GH5-tCel5A1 reported by [PERSON] and [PERSON] [127] and the porcine gut GH5-p4818 Cel5_2A endoglucanase reported by [PERSON] et al. [45] had an excellent hydrolytic activity on pure crystalline cellulose substrates in comparison with a number of bacterial endocellulaes reported in the literature. On the other hand, we should also compare the GH5-tCel5A1 and the GH5-p4818 Cel5_2A processive endoglucanase properties, as reported by [PERSON] and [PERSON] [127] and [PERSON] et al. [45], with the following two thermophilic (i.e., 45-122 \({}^{\circ}\)C) processive endocellulaes of bacterial origins that are highly regarded for their potential industrial applications with high endocellalase activities in hydrolyzing crystalline cellulosic substrates in the current literature. The _Clostridium Phytorementans_ GH9 processive endoglucanase Cel9 was cloned and characterized to have about 11-fold higher specific activity (2.488 umol D-glucose/mg protein.min) determined with Avicel by [PERSON] et al. [135] than GH5-p4818 Cel5_2A. _Clostridium Phytorementans_ is an obligately anaerobic, mesophilic (i.e., 20-45 \({}^{\circ}\)C), cellulolytic Gram-positive bacterium strain (i.e., \(\text{ISD}_{\text{g}}^{\text{T}}\) = ATCC 700394\({}^{\text{T}}\)) isolated from forest soil by [PERSON] et al. [136].