Immobilization of fungal laccase onto red seaweed biomass as a novel support for efficient dye decolorization

Abstract

In this study, the indigenous white rot fungal strain Hebeloma sp. YZH2 was isolated and identified based on the 18S rRNA gene sequencing technique. This fungal strain was used for laccase production under submerged fermentation of wheat bran. The produced crude fungal laccase was immobilized onto Gracilaria, which was used as a novel support matrix for laccase immobilization for the first time. The fungal laccase immobilized on Gracilaria (LIG) was then applied for the decolorization of the textile azo dye Eriochrome Black T (EBT) from aqueous solutions. LIG was further optimized to achieve maximum dye decolorization through response surface methodology using the Box- Behnken design (BBD). The results indicated that the fungal strain Hebeloma sp. YZH2 exhibited high laccase production under submerged fermentation of wheat bran and laccase activity reached a peak of 293.8 U/mL after 26 days of incubation. Laccase was successfully immobilized onto Gracilaria biomass by adsorption method followed by precipitation and cross-linking. The maximum immobilized laccase activity of 199.3 U/g was observed at 200 U/mL, 5 %, 2 h and 10 mM for laccase concentration, Gracilaria concentration, cross- linking time, and glutaraldehyde concentration, respectively. LIG showed high thermal stability, retaining 31 % relative activity at 80°C, while free laccase completely lost its activity. It also showed better pH stability compared to free laccase. Based on BBD results, the maximum predicted EBT decolorization efficiency (99.27 %) was achieved at pH 4.04, agitation speed of 159.29 rpm and biomass dose of 9.84 g/L.