Degradation and Detoxification of Congo Red azo dye by Immobilized Laccase of Streptomyces sviceus

Abstract

The discharge of textile effluents enriched with reactive azo dyes is of critical importance owing to inability of the dyes to degrade in waste water and their carcinogenic, mutagenic effects to various organisms. This study initiated based on the need to gaze into molecular mechanism of marine bacterial bioremediation process to develop strategies for the decolorization and detoxification of the synthetic azo dyes. The experimental work carried out to explore decolorization and degradation efficacy of laccase derived from marine actinobacteria, Streptomyces sviceus by choosing Congo red-21 as model azo dye. The extracellular production of laccase was confirmed with plate assay in medium supplemented with ABTS as substrate. Laccase was purified to homogeneity from 72hrs culture of Streptomyces sviceus by Fast performance liquid chromatography and the molecular size of laccase was noticed as 60 kDa. The purified laccase was immobilized with an efficiency of 82% by Calcium alginate method. The crude, purified and immobilized forms of the laccase enzyme was used to decolorize the Congo red-21. Crude laccase enzyme showed 69% of decolorization of Congo red-21 after 48h where as purified and immobilized laccase represented 78% and 92% of colour removal after 24 h respectively. Fourier-transform infrared spectroscopy, High Performance Liquid Chromatography and Gas chromatography–mass spectrometry were used to unravel the molecular mechanism of dye detoxification and also identify nontoxic products released from Congo Red-21 upon administration with immobilized laccase. Based on GC-MS data, it may deduce that immobilized laccase of Streptomyces sviceus cleaves the Congo red-21 dye followed by oxidative cleavage, desulfonation, deamination, demethylation process.

Keywords

• marine bacteria
• reactive azo dyes
• decolorization
• streptomyces sviceus
• immobilized laccase