A Halophilic, Alkalithermostable, Ionic Liquid-Tolerant Cellulase and Its Application in In Situ Saccharification of Rice Straw

A cellulase, En5H, from halophilic, alkalithermophilic Alkalilimnicola sp. NM-DCM1 was expressed and purified. En5H had maximal hydrolytic activity at 55 A degrees C, pH 8.8, and 2.5 M NaCl. En5H is beta-1,4 linkage-specific, hydrolyzing carboxymethyl cellulose, Avicel, cellobiose, and p-nitrophenyl beta-d-glucopyranoside. En5H was resistant to inhibitors and organic solvents. The half-life of En5H was increased 16-43-fold when incubated in 20% (v/v) of ionic liquids (IL) at 55 A degrees C in the presence of 2.5 M NaCl, and maximal hydrolytic activity of En5H in 10% (v/v) 1-allyl-3-methylimidazolium chloride and 1,3-dimethylimidazolium dimethyl phosphate was 122 and 110%, respectively, as compared with activity in buffer. A cellulase-IL system combining IL pretreatment and enzymatic saccharification was tested. With an enzyme load of 110 U/g rice straw, the conversion of rice straw cellulose and hemicellulose increased by 28% compared with unpretreated rice straw. En5H has potential for use in transformation of lignocellulose to glucose in a single-step process.