Screening of five marine-derived fungal strains for their potential to produce oxidases with laccase activities suitable for biotechnological applications

Abstract

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 marinederived 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 1hydroxybenzotriazole (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.

Characterization of the CAZy Repertoire from the Marine-Derived Fungus Stemphylium lucomagnoense in Relation to Saline Conditions

“…For cellulase activities, no significant differences could be seen, probably because the standard deviations were high in our test conditions. It would appear that cellulase activities were higher in cultures grown on seagrass in non-saline conditions ( Figure 2B), and that T. asperellum and A. nidulans, showed the highest ones For laccase-like activities ( Figure 2C), results show that globally in saline condition, the culture medium reduced the secretome activities for all strains except for S. lucomagnoense cultured on seagrass, confirming our previous results [22]. In general, the three T. asperellum strains showed the highest activities, and A. nidulans the lowest.…”

“…The radial growth of five fungal strains isolated from marine environments [ 22 ], namely, Stemphylium lucomagnoense, Aspergillus nidulans, and three Trichoderma asperellum strains (called T. asperellum 1 (Tas 1), T. asperellum 2 (Tas 2) and T. asperellum 3 (Tas 3)), was evaluated. We followed and compared fungal growth on two different carbon sources, xylan, and carboxymethylcellulose (CMC), in the presence or absence of sea salt ( Figure 1 ).…”

“…The objective of the present study was to provide new insight into the lignocellulose enzyme machinery of marine-derived fungi, to understand how they adapted to process biomass in saline conditions. For this purpose, we screened five fungal strains isolated from the Tunisian coast [22]. Based on a microbial approach and on enzyme activity screening, we selected S. lucomagnoense for its adapted growth on xylan in saline conditions, its higher xylanase activity, and its improved laccase (seagrass-containing cultures) and cellulase (wheat straw-containing cultures) activities in the presence of sea salt.…”

“…The main objectives of our work were to get insight into lignocellulose degradation by marine-derived fungi and to assess whether and how fungal enzymatic machineries adapt to saline conditions. In a previous study, five marine-derived fungal strains were isolated from Tunisian coasts and identified by a phylogenetic approach, and the adaptation of laccase-like activities in their secretome was assessed, in response to several factors, including salt conditions [22]. In this work, we study the growth of the five isolates and the tuning of lignocellulolytic activities under different conditions.…”

Large-scale phenotyping of 1,000 fungal strains for the degradation of non-natural, industrial compounds

“…Despite their poor e ciency on LGS and AVI, brown-rot fungi proved to be able to decolorize synthetic dyes, notably BB41. It is known that fungal laccases (with redox mediators) and peroxidases can bleach RB5 [36][37][38] whereas only peroxidases have hitherto been shown to discolor BB41 39,40 . Brown-rot fungi being devoid of ligninolytic peroxidases 28 , they probably act on BB41 via other systems, involving either Fenton or other types of haem-peroxidases 41 .…”