Bio-chemical characterization of a β-mannanase from Bacillus licheniformis HDYM-04 isolated from flax water-retting liquid and its decolorization ability of dyes

Abstract

A β-mannanase was purified from the bacteria, Bacillus licheniformis HDYM-04, which was a high β-mannanase-producing strain (576.16 U mL⁻¹ at 48 h during fermentation). The optimal temperature and pH for this enzyme activity were 60 °C and 8.0, respectively. The enzyme activity was significantly enhanced by Co²⁺, Mg²⁺, K⁺, Ba²⁺ and Na⁺ while inhibited by β-mercaptoethanol, DTT, SDS, Tween and EDTA. It was also noticed that the enzyme did not lose its activity in a wide interval such as high NaCl concentration (5 mol L⁻¹) and high urea concentration (5 mol L⁻¹). When amino acid residues were modified with NEM, N-AI and NBS, the enzyme activities significantly decreased. CD spectra demonstrated that the secondary structure of β-mannanase consists of 0% α-helix, 27.9% β-sheet, 24.4% turn and 47.7% random coil. CD spectra also supported that β-mannanase was stable under temperature and pH variation. Ten structurally different dyes could be effectively decolorized by β-mannanase within 24 h, in which Congo red (100%), malachite green (100%), titan yellow (98.6%) and phenol red (91%) had high decolorization rates. This property showed the compound's potential application in textile and paper-making industries to decolorize redundant dyes on them.