Overexpression of a novel thermostable and chloride-tolerant laccase from Thermus thermophilus SG0.5JP17-16 in Pichia pastoris and its application in synthetic dye decolorization.

Laccases have been used for the decolorization and detoxification of synthetic dyes due to their ability to oxidize a wide variety of dyes with water as the sole byproduct. A putative laccase gene (LacTT) from Thermus thermophilus SG0.5JP17-16 was screened using the genome mining approach， and it was highly expressed in Pichia pastoris， yielding a high laccase activity of 6130 U/L in a 10-L fermentor. The LacTT open reading frame encoded a protein of 466 amino acid residues with four putative Cu-binding regions. The optimal pH of the recombinant LacTT was 4.5， 6.0， 7.5 and 8.0 with 2，2'-azino-bis(3-ethylbenzothazoline-6-sulfonic acid) (ABTS)， syringaldazine (SGZ)， guaiacol， and 2，6-dimethoxyphenol (2，6-DMP) as the substrate， respectively. The optimal temperature of LacTT was 90°C with guaiacol as the substrate. LacTT was highly stable at pH 4.0-11.0 and thermostable at 40°C-90°C， confirming that it is a pH-stable and thermostable laccase. Furthermore， LacTT also exhibited high tolerance to halides such as NaCl， NaBr and NaF， and decolorized 100%， 94%， 94% and 73% of Congo Red， Reactive Black B and Reactive Black WNN， and Remazol Brilliant Blue R， respectively. Interestingly， addition of high concentration of NaCl increased the RBBR decolorization efficiency of LacTT. These results suggest that LacTT is a good candidate for industrial applications such as dyestuff processing and degradation of dyes in textile wastewaters.