A Halotolerant Endo-1,4-β-Xylanase from Aspergillus clavatus with Potential Application for Agroindustrial Residues Saccharification

Abstract

The use of non-potable water (such as seawater) is an attractive alternative for water intensive processes such as biomass pretreatment and saccharification steps in the production of biochemicals and biofuels. Identification and application of halotolerant enzymes compatible with high-salt conditions may reduce the energy needed for non-potable water treatment and decrease waste treatment costs. Here we present the biochemical properties of a halotolerant endo-1,4-β-xylanase produced by Aspergillus clavatus in submerged fermentation, using paper sludge (XPS) and sugarcane bagasse (XSCB), and its potential application in the hydrolysis of agroindustrial residues. The peptide mass fingerprint and amino acid sequencing of the XPS and XSCB enzymes showed primary structure similarities with an endo-1,4-β-xylanase from Aspergillus clavatus (XYNA_ASPCL). Both enzyme preparations presented good thermal stability at 50 °C and were stable over a wide range of pH and V_max up to 2450 U/mg for XPS. XPS and XSCB were almost fully stable even after 24 h of incubation in the presence of up to 3 M NaCl, and their activity were not affected by 500 mM NaCl. Both enzyme preparations were capable of hydrolyzing paper sludge and sugarcane bagasse to release reducing sugars. These characteristics make this xylanase attractive to be used in the hydrolysis of biomass, particularly with brackish water or seawater.

Keywords: Aspergillus; Bioethanol; Halotolerant enzyme; Paper sludge; Phylogenetic relationship; Sequence alignment; Three-dimensional modeling; Xylanase.