Screening of marine fungal strains for laccase-like activities amenable to biotechnological applications

Abstract

Background Environmental pollution is one of the major problems that world is facing to date. Several approaches are been studied and oxidative enzymes from microbial organisms represent an eco-friendly and cost–effective processes, amenable to biotechnological applications, as for instance industrial dye decolorization. The aim of this study was to screen marine-derived fungal strains isolated from three coastal areas in Tunisia, to identify laccase-like activities, and to produce and characterize active fungal secretomes of interest for dye decolorization. Results Following the screening of twenty fungal strains isolated from the harbours of Sfax and Monastir (Tunisia), five strains were identified displaying laccase-like activities. Molecular based taxonomic approaches allowed us to identify these strains as belonging to the species Trichoderma asperellum , Stemphylium lucomagnoense and Aspergillus nidulans . Among these five isolates, one T. asperellum strain ( T. asperellum 1) gave the highest level of secreted oxidative activities, and as such it was chosen for further studies. Optimization of the growth medium for liquid cultures was first studied to improve the level of laccase-like activity in culture supernatants. Finally, T. asperellum 1 secretome allowed decolorizing different synthetic dyes belonging to diverse dye families, in the presence or absence of 1-hydroxybenzotriazole (HBT) as a mediator. Conclusions The optimal growth conditions to produce laccase-like active secretomes from T. asperellum 1 were 1.8 mM CuSO 4 as an inducer, 1% NaCl to mimic seawater environment and 3% sucrose as a carbon source. T. asperellum 1 secretome was effective to decolorize different synthetic dyes belonging to diverse chemical classes, and the presence of HBT as a mediator improved the decolorization process.