Characterization of a halostable endoglucanase with organic solvent-tolerant property from Haloarcula sp. G10.

A haloarchaeal strain G10 with celluolytic activity was isolated from the saline soil of Yuncheng Salt Lake, China. Biochemical and physiological characterization along with 16S rRNA gene sequence analysis placed the isolate in the genus Haloarcula. The extracellular cellulase was purified to homogeneity with a molecular mass of 36 kDa. Substrate specificity test indicated that it was an endoglucanase for soluble cellulose. Optimal enzyme activity was found to be at 60 °C, pH 9.0 and 17.5% NaCl. Furthermore, high activity and stability over broad ranges of temperature (40-80 °C), pH (7.0-10.0) and NaCl concentration (12.5-27.5%) were observed, showing thermostable, alkali-stable and halostable properties of the cellulase. Significant inhibition by EDTA, phenylmethylsulfonyl fluoride (PMSF) and diethyl pyrocarbonate (DEPC) revealed it was a metalloenzyme with serine and histidine residues essential for enzyme catalysis. The surfactants tested had little effects on the enzyme activity. The endoglucanase showed high activity and stability in the presence of non-polar hydrophobic organic solvents with log Pow≥0.88. Together these results indicated the cellulase from Haloarcula sp. G10 maybe an ideal choice for applications in industrial process under harsh conditions.