SUMMARY
Background: Endoglucanase plays a major role in initiating cellulose hydrolysis. Various wild-type strains were
searched to produce this enzyme, but mostly low extracellular enzyme activities were obtained. To improve
extracellular enzyme production for potential industrial applications, the endoglucanase gene of Bacillus
subtilis M015, isolated from Thai higher termite, was expressed in a periplasmic-leaky Escherichia coli. Then,
the crude recombinant endoglucanase (EglS) along with a commercial cellulase (Cel) was used for hydrolyzing
celluloses and microbial hydrolysis using whole bacterial cells.
Results: E. coli Glu5 expressing endoglucanase at high levels was successfully constructed. It produced EglS
(55 kDa) with extracellular activity of 18.56 U/mg total protein at optimal hydrolytic conditions (pH 4.8 and
50°C). EglS was highly stable (over 80% activity retained) at 40–50°C after 100 h. The addition of EglS
significantly improved the initial sugar production rates of Cel on the hydrolysis of carboxymethyl cellulose
(CMC), microcrystalline cellulose, and corncob about 5.2-, 1.7-, and 4.0-folds, respectively, compared to those
with Cel alone. E. coli Glu5 could secrete EglS with high activity in the presence of glucose (1% w/v) and Tween
80 (5% w/v) with low glucose consumption. Microbial hydrolysis of CMC using E. coli Glu5 yielded 26 mg
reducing sugar/g CMC at pH 7.0 and 37°C after 48 h.
Conclusions: The recombinant endoglucanase activity improved by 17 times compared with that of the native
strain and could greatly enhance the enzymatic hydrolysis of all studied celluloses when combined with a
commercial cellulase.