Expression and characterization of novel laccase gene from Pandoraea sp. ISTKB and its application

In the present study, a non-blue laccase gene from previously reported lignin degrading bacterium, Pandoraea sp. ISTKB, was isolated, cloned and expressed in E. coli. Bioinformatics analysis of sequence discovered twin-arginine translocation signal sequence, copper binding motifs and presence of more random coil compare to helices and sheets in structure. The enzyme was found to be active on wide pH range and the pH optima was observed at pH 4 and 8 on substrate 2,2'-Azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) and 2,6-Dimethoxyphenol respectively. This is a thermophilic enzyme with maximum activity around 50-70 °C. The enzyme was further characterized by spectroscopy, reaction kinetics and effect of metal ions and inhibitors were studied. Compared to laccase alone; the treatment of dyes with laccase plus mediator resulted in enhanced decolorization of crystal violet, methylene blue, azure B, carmine and Congo red but the effect of mediator was not observed on trypan blue. Laccase treatment triggered polymerization on vanillic acid (VA) and kraft lignin (KL). Laccase plus mediator treatment reversed the polymerization and resulted in transformation or degradation of VA and KL. This thermophilic and alkalophilic non-blue laccase from Pandoraea sp. ISTKB is promising with prospective biotechnological application.