A novel homodimer laccase from Cerrena unicolor BBP6: Purification, characterization, and potential in dye decolorization and denim bleaching.

Ji Zhang,Xiaoyu Zhang,Shufang Wang,Anli Geng,Hao Zhang,Lei Sun,Travis Beddoe

doi:10.1371/journal.pone.0202440

Abstract

The white-rot fungus Cerrena unicolor BBP6 produced up to 243.4 U mL-1 laccase. A novel laccase isoform LacA was purified; LacA is a homodimer with an apparent molecular mass of 55 kDa and an isoelectric point of 4.7. Its optimal pH was 2.5, 4.0, and 5.5 when 2, 2’-Azinobis-(3-ethylbenzthiazoline-6-sulphonate) (ABTS), guaiacol, and 2, 6-dimethoxyphenol (2, 6-DMP) were used as the substrates, respectively. The optimal temperature was 60°C for ABTS and 80°C for both guaiacol and 2, 6-DMP. LacA retained 82–92% activity when pH was greater than 4 and 42%-92% activity at or below 50°C. LacA was completely inhibited by 0.1 mM L-cysteine, 1 mM Dithiothreitol, and 10 mM metal ions, Ca2+, Mg2+ and Co2+. LacA had good affinity for ABTS, with a Km of 49.1 μM and a kcat of 3078.9 s-1. It decolorized synthetic dyes at 32.3–87.1%. In the presence of 1-hydroxybenzotriazole (HBT), LacA decolorized recalcitrant dyes such as Safranine (97.1%), Methylene Blue (98.9%), Azure Blue (96.6%) and simulated textile effluent (84.6%). With supplemented manganese peroxidase (MnP), Mn2+ and HBT, the purified LacA and BBP6 fermentation broth showed great potential in denim bleaching, with an up to 5-fold increase in reflectance values.

Highlights

White-rot fungi has an exceptional ability to produce extracellular oxidative enzymes, which is involved in lignin degradation
This study reports the production, purification, and characterization of a novel laccase from a new white-rot fungus strain C. unicolor BBP6 and the application of its laccase in decolorization of recalcitrant dyes and denim bleaching
Greater than 82% Azure B decolorization was obtained using a much lower laccase concentration (500 U L-1) and higher Azure B concentration (50 mg L-1) (Table 6). These results suggest that LacA has great potential in recalcitrant dye decolorization

Summary

Introduction

White-rot fungi has an exceptional ability to produce extracellular oxidative enzymes, which is involved in lignin degradation. In the presence of synthetic or natural compounds that act as redox mediators, such as 1-hydroxybenzotrizole (HBT), syringaldehyde, acetosyringone and vanillin, the spectrum of laccase oxidizable substrates can be expanded considerably toward nonphenolic and more recalcitrant pollutants [6,7,8] Due to their interesting catalytic properties and broad substrate specificities, laccases have many actual and potential applications in a variety of industrial fields, including paper-pulp/textile bleaching, food, pharmaceutical and cosmetic industries, bioremediation and biosynthesis [3, 9,10,11]. This study reports the production, purification, and characterization of a novel laccase from a new white-rot fungus strain C. unicolor BBP6 and the application of its laccase in decolorization of recalcitrant dyes and denim bleaching

Materials and methods

10 U mL-1 LacA

Conclusion