A novel thermostable and halotolerant xylanase from Colletotrichum graminicola

A novel endoxylanase from Colletotrichum graminicola (Excg1) was purified. Similar apparent molecular masses were estimated by gel filtration (17.3 ± 1.9 kDa) and sodium dodecyl sulfate polyacrylamide gel electrophoresis (20.0 ± 2.4 kDa), suggesting that Excg1 is monomeric. The enzyme showed good halotolerance, retaining about 85% and 50% of the control activity in the presence of 0.5 mol L−1 and 3.0 mol L−1 NaCl, respectively. The optimum temperature of Excg1 (65 °C) was not affected by NaCl, but the optimum pH rose from 5.5 in the absence and presence of 0.5 mol L−1 NaCl to 6.0, in 2.5 mol L−1 NaCl. Excg1 was highly thermostable at 50 °C, with half-lives around 48 h in either water or 0.5 mol L−1 NaCl and a residual activity of 75% at 2.5 mol L−1 NaCl. Excg1 was fully stable at pH 3.0–10.0 in the absence of salt, and from pH 4.0–10.0 in the presence of 0.5 mol L−1 and 2.5 mol L−1 NaCl. The enzyme hydrolyzed beechwood xylan with maximal velocity and apparent affinity constant of 481.3 ± 34.0 U mg−1 and 3.7 ± 0.3 mg mL−1, respectively. Similar kinetic parameters were obtained in the presence of 0.5 mol L−1 NaCl, but a maximum velocity about 34% lower was determined in 2.5 mol L−1 NaCl. Excg1 was tolerant to various organic solvents at a concentration of 5% (w/v) and also to sodium acetate up to 200 mmol L−1. Xylobiose and xylotriose with a 4-O-methylglucuronic acid branching were the main products of beechwood xylan hydrolysis, and the time course of hydrolysis was not affected by NaCl 0.5 mol L−1 or sea water. To the best of our knowledge, this is the first report of a halotolerant endoxylanase from fungal origin. The properties of Excg1 suggested good potential for use in lignocellulose saccharification processes particularly using sea water or under high salt conditions, or in the presence of residues and/or byproducts of pretreatment steps, contributing to improve the economic viability of 2G ethanol production. © 2017 Elsevier B.V.