Background: Environmental pollution is one of the major problems that the world is facing today. Several approaches have been taken, from physical and chemical methods to biotechnological strategies (e.g. the use of oxidoreductases). Oxidative enzymes from microorganisms offer eco-friendly, cost–effective processes amenable to biotechnological applications, such as in 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 cell-free supernatants of interest for dye decolorization. Results: Following the screening of 20 fungal strains isolated from the harbors of Sfax and Monastir (Tunisia), five strains were identified that displayed laccase-like activities. Molecular-based taxonomic approaches identified 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 so was chosen for further studies. Optimization of the growth medium for liquid cultures was first undertaken to improve the level of laccase-like activity in culture supernatants. Finally, the culture supernatant of T. asperellum 1 decolorized 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 cell-free supernatants from T. asperellum 1 were 1.8 mM CuSO₄ as an inducer, 1% NaCl to mimic a seawater environment and 3% sucrose as a carbon source. The culture supernatant of T. asperellum 1 effectively decolorized different synthetic dyes belonging to diverse chemical classes, and the presence of HBT as a mediator improved the decolorization process.

Only a few studies have examined how marine-derived fungi and their enzymes adapt to salinity and plant biomass degradation. This work concerns the production and characterisation of an oxidative enzyme identified from the transcriptome of marine-derived fungus Stemphylium lucomagnoense. The laccase-encoding gene SlLac2 from S. lucomagnoense was cloned for heterologous expression in Aspergillus niger D15#26 for protein production in the extracellular medium of around 30 mg L⁻¹. The extracellular recombinant enzyme SlLac2 was successfully produced and purified in three steps protocol: ultrafiltration, anion-exchange chromatography, and size exclusion chromatography, with a final recovery yield of 24%. SlLac2 was characterised by physicochemical properties, kinetic parameters, and ability to oxidise diverse phenolic substrates. We also studied its activity in the presence and absence of sea salt. The molecular mass of SlLac2 was about 75 kDa, consistent with that of most ascomycete fungal laccases. With syringaldazine as substrate, SlLac2 showed an optimal activity at pH 6 and retained nearly 100% of its activity when incubated at 50°C for 180 min. SlLac2 exhibited more than 50% of its activity with 5% wt/vol of sea salt.

Even if the ocean represents a large part of Earth’s surface, only a few studies describe marine-derived fungi compared to their terrestrial homologues. In this ecosystem, marine-derived fungi have had to adapt to the salinity and to the plant biomass composition. This articles studies the growth of five marine isolates and the tuning of lignocellulolytic activities under different conditions, including the salinity. A de novo transcriptome sequencing and assembly were used in combination with a proteomic approach to characterize the Carbohydrate Active Enzymes (CAZy) repertoire of one of these strains. Following these approaches, Stemphylium lucomagnoense was selected for its adapted growth on xylan in saline conditions, its high xylanase activity, and its improved laccase activities in seagrass-containing cultures with salt. De novo transcriptome sequencing and assembly indicated the presence of 51 putative lignocellulolytic enzymes. Its secretome composition was studied in detail when the fungus was grown on either a terrestrial or a marine substrate, under saline and non-saline conditions. Proteomic analysis of the four S. lucomagnoense secretomes revealed a minimal suite of extracellular enzymes for plant biomass degradation and highlighted potential enzyme targets to be further studied for their adaptation to salts and for potential biotechnological applications.

Background : Environmental pollution is one of the major problems that the world is facing today. Several approaches have been taken, from physical and chemical methods to biotechnological strategies (e.g. the use of oxidoreductases). Oxidative enzymes from microorganisms offer eco-friendly, cost–effective processes amenable to biotechnological applications, such as in 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 cell-free supernatants of interest for dye decolorization.Results : Following the screening of 20 fungal strains isolated from the harbors of Sfax and Monastir (Tunisia), five strains were identified that displayed laccase-like activities. Molecular-based taxonomic approaches identified 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 so was chosen for further studies. Optimization of the growth medium for liquid cultures was first undertaken to improve the level of laccase-like activity in culture supernatants. Finally, the culture supernatant of T. asperellum 1 decolorized 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 cell-free supernatants from T. asperellum 1 were 1.8 mM CuSO 4 as an inducer, 1% NaCl to mimic a seawater environment and 3% sucrose as a carbon source. The culture supernatant of T. asperellum 1 effectively decolorized different synthetic dyes belonging to diverse chemical classes, and the presence of HBT as a mediator improved the decolorization process.

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.