Decolorization of complex dyes and textile effluent by extracellular enzymes of Cyathus bulleri cultivated on agro-residues/domestic wastes and proposed pathway of degradation of Kiton blue A and reactive orange 16

Abstract

In this study, the white-rot fungus Cyathus bulleri was cultivated on low-cost agro-residues, namely wheat bran (WB), wheat straw (WS), and domestic waste orange peel (OP) for production of ligninolytic enzymes. Of the three substrates, WB and OP served as good materials for the production of laccase with no requirement of additional carbon or nitrogen source. Specific laccase activity of 94.4 U mg⁻¹ extracellular protein and 21.01 U mg⁻¹ protein was obtained on WB and OP, respectively. Maximum decolorization rate of 13.6 μmol h⁻¹ U⁻¹ laccase for reactive black 5 and 22.68 μmol h⁻¹ U⁻¹ laccase for reactive orange 16 (RO) was obtained with the WB culture filtrate, and 11.7 μmol h⁻¹ U⁻¹ laccase for reactive violet 5 was observed with OP culture filtrate. Importantly, Kiton blue A (KB), reported not to be amenable to enzymatic degradation, was degraded by culture filtrate borne activities. Products of degradation of KB and RO were identified by mass spectrometry, and a pathway of degradation proposed. WB-grown culture filtrate decolorized and detoxified real and simulated textile effluents by about 40%. The study highlights the use of inexpensive materials for the production of enzymes effective on dyes and effluents.