Identification and characterization of halotolerant multifunctional GH6 endoglucanases ZFEG1605 and ZFEG1663 from Mt. Everest soil metagenome

Environmental microorganisms express enzymes with unique hydrolytic activity, stability, and kinetic parameters, which are of great interest for biotechnological applications. In this study, two novel endoglucanases, ZFEG1605 and ZFEG1663, were cloned from Mt. Everest soil metagenomic library, heterologously expressed in E. coli BL21(DE3), and characterized. Both enzymes exhibited high activity on konjac glucommanan (KG) and sodium carboxymethylcellulose (CMC), while ZFEG1605 also exhibited activity towards guar gum (GG). The optimal pH for both enzymes was slightly shifted toward acidic range (pH 5/6). The optimal reaction temperatures for ZFEG1605 and ZFEG1663 were 50 and 40 °C, respectively. ZFEG1605 was more thermostable than ZFEG1663 as it remained stable up to 50 °C, compared to 40 °C for ZFEG1663. Both enzymes showed broad pH stability, although they retained more mannanase activity than CMCase activity within the same pH range. The endoglucanases exhibited remarkable salt tolerance, retaining over 70 % of their enzymatic activity in the presence of 2.5 M NaCl. The purified enzymes hydrolyzed alkali-pretreated rice straw to release reducing sugars, demonstrating their potential usage for biomass saccharification.