The unique GH5 cellulase member in the extreme halotolerant fungus Aspergillus glaucus CCHA is an endoglucanase with multiple tolerance to salt, alkali and heat: prospects for straw degradation applications

Abstract

In a halotolerant fungus Aspergillus glaucus CCHA, several functional proteins with stress-tolerant activity have been studied, but no secretory enzymes have been identified yet. The unique GH5 cellulase candidate from A. glaucus, an endoglucanase termed as AgCMCase, was cloned, expressed in the Pichia pastoris system and the purified enzyme was characterized. A large amount of recombinant enzyme secreted by the P. pastoris GS115 strain was purified to homogeneity. The molecular weight of the purified endoglucanase is about 55.0 kDa. The AgCMCase exhibited optimum catalytic activity at pH 5.0 and 55 °C. However, it remained relatively stable at temperatures ranging from 45 to 80 °C and pH ranging from 4.0 to 9.0. In addition, it showed higher activity at extreme NaCl concentrations from 1.0 to 4.0 M, suggesting it is an enzyme highly stable under heat, acid, alkaline and saline conditions. To evaluate the catalytic activity of AgCMCase, the hydrolysis products of rice and corn straws were successfully studied. In conclusion, the AgCMCase is a thermostable and salt-tolerant cellulase with potential for industrial application.

Biochemical characterization of a novel thermo‐halo‐tolerant GH5 endoglucanase from a thermal spring metagenome

“…The desired thermo‐ and halotolerance/stability‐related properties of Cel M were discerned to be better than many previously reported proteins characterized as thermo‐halo‐tolerant endoglucanases from Thermobifida halotolerans (Yin et al, 2015), Botrytis ricini (Silva et al, 2018), Bacillus sp. (Aygan and Akiran, 2008), Icelandic hot spring isolate (Zarafeta et al, 2016), A. glaucus (Li et al, 2018), and Thermoanaerobacter tengcongensis (Liang et al, 2011; Table 2). However, with a comparable level of halotolerance as that of Cel M , the endoglucanase from Dictyoglomus thermophilum had been found to be excessively thermostable, exhibiting the half‐life of about 336 h at 70°C (Shi et al, 2013).…”

“…Many fungal and bacterial strains have been characterized for endoglucanase production; however, enzymes of bacterial origin could offer some advantages associated with its ability to thrive in harsh environments, relatively faster growth, and a better yield of the recombinant enzyme. Some of the recently reported GH5 endoglucanases are from Bacillus subtilis 1AJ3 (Ma et al, 2020), Thermoactinospora rubra YIM 77501T (Yin et al, 2020), Cellulomonas bogoriensis 69B4T (Li et al, 2020), Thermobifida alba AHK119 (Ohta et al, 2019), Aspergillus glaucus CCHA (Li et al, 2018), Saccharophagus degradans 2‐40T (Wang et al, 2016), Jonesia quinghaiensis (Lin et al, 2016), cow rumen metagenome (Patel et al, 2020), termite gut metagenome (Guerrero et al, 2020), porcine gut metagenome (Wang et al, 2019), rhizosphere metagenome (Wierzbicka‐Wos et al, 2019), soil metagenome (Kumar et al, 2019; Pimentel et al, 2017), hot spring metagenome (Gupta et al, 2017; Zarafeta et al, 2016), and so forth.…”

An Archaeal Chitinase With a Secondary Capacity for Catalyzing Cellulose and Its Biotechnological Applications in Shell and Straw Degradation

“…However, this enzyme has low catalysis activity for β-1,3-1,4- linkages, such as that found in glucan. In addition, Tk-ChiA degraded Avicel, a type of crystalline cellulose (approximately 60% activity compared to chitosan), indicating that it has dual exo-1,4-β-glucanases and endo-1,4-β-glucanases functions (Park et al, 2012; Li et al, 2018).…”

“…However, cellulose is the major polysaccharide of plant cell walls and is thus the most abundant natural polymer. Cellulose is present in various types of straw and is a valuable natural resource (Li et al, 2018). Approximately, 10 14 –10 15 tons of cellulose is produced annually in the form of raw materials derived from straw, wood, cotton, reeds, hemp, and mulberry (Bayer et al, 1998; Zarafeta et al, 2016).…”

A novel high performance in-silico screened metagenome-derived alkali-thermostable endo-β-1,4-glucanase for lignocellulosic biomass hydrolysis in the harsh conditions

“…Furthermore, pretreatment with high concentrations of NaCl improved the enzyme's activity [17]. A novel GH5 cellulase from Aspergillus glaucus with high stability under heat, acid, alkaline and saline conditions and ability to degrade lignocellulosic feedstock demonstrated the high potential in biomass and industrial application [18]. Also, a novel acid/ alkali and thermo tolerant cellulase with high ability in agro residues saccharification reported as a candidate for bioethanol production [19].…”