Light-induced expression of a novel marine laccase in Escherichia coli from Marinomonas profundimaris and its application in synthetic dye decolorization

Abstract

Laccases (EC 1.10.3.2) are green biocatalysts with a considerable potential in numerous environmental and industrial applications due to their abilities to oxidize a wide range of substrates, such as aromatic amines, while reducing molecular oxygen to water. In this study, a putative laccase, LacMp1, encoding a protein of 48.3 kDa and belonging to the Cu-oxidase_3 superfamily, was cloned and overexpressed in Escherichia coli with a light-induced expression system. High-level expression of recombinant protein LacMp1 was achieved under the light intensity of 6500 ± 200 lx from a white light-emitting diode (LED) belt. The purified LacMp1 showed high activity toward various laccase substrates, with the lowest K_m value and highest k_cat/K_m value for syringaldazine at the optimal temperature and pH of 50 °C and 7.5. Dimethyl sulfoxide, ethanol, and metal ions such as Co²⁺, Ca²⁺, K⁺, Li⁺, Zn²⁺, Mn²⁺, Fe³⁺, and Ni²⁺ did not significantly inhibit the activity of LacMp1. Furthermore, LacMp1 showed tolerance to NaCl and kept 66.67 ± 2.24% of its initial activity at concentrations lower than 400 mM. Moreover, LacMp1 exhibited wide-spectrum decolorization ability towards indigoid, anthraquinonic, and azo dyes without the aid of redox mediators at pHs ranging from 5.0 to 9.0. It decolorized 99.83 ± 0.12% of indigo carmine, 99.54 ± 0.43% of Congo red, 88.41 ± 3.22% of Eriochrome black T, and 51.61 ± 1.82% of Reactive blue 4, respectively. These unusual properties demonstrated that LacMp1 had potential in specific industrial or environmental applications.

Keywords: Dye decolorization; Escherichia coli; Laccase; Light-induced expression system; Marinomonas profundimaris; Redox mediator.