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

A novel endoglucanase gene, celM , was cloned from a thermal spring metagenome. The gene was expressed in Escherichia coli, and the protein was extracted and purified. The protein catalyzed the hydrolysis of amorphous cellulose in a wide range of temperatures, 30-95°C, with optimal activity at 80°C. It was able to tolerate high temperature (80°C) with a half-life of 8 h. Its activity was eminent in a wide pH range of 3.0-11.0, with the highest activity at pH 6.0. The enzyme was tested for halostability. Any significant loss was not recorded in the activity of CelM after the exposure to salinity (3 M NaCl) for 30 days. Furthermore, CelM displayed a substantial resistance toward metal ions, denaturant, reducing agent, organic solvent, and non-ionic surfactants. The amorphous cellulose, treated with CelM , was randomly cleaved, generating cello-oligosaccharides of 2-5 degree of polymerization. Furthermore, CelM was demonstrated to catalyze the hydrolysis of cellulose fraction in the delignified biomass samples, for example, sweet sorghum bagasse, rice straw, and corncob, into cello-oligosaccharides. Given that CelM is a thermo-halo-tolerant GH5 endoglucanase, with resistance to detergents and organic solvent, the biocatalyst could be of potential usefulness for a variety of industrial applications.