Exploring the soil mangrove diversity for new fungal DyPs

We recently investigated the structural organization of fungi in mangrove sediments of New Caledonia. In the present work, the objective was to extend this research by studying the functional diversity of the same mangrove sediments, i.e. getting data of fungal enzymes involved in the decomposition of the dead biomass accumulated in the sediments, together with their complete biochemical characterization. The diversity of expressed genes encoding fungal DyPs was investigated in surface and deeper mangrove sediments beneath Avicennia marina and Rhizophora stylosa trees during the wet and dry seasons using a functional metabarcoding approach. For instance, DyP diversity was demonstrated to be higher in surface beneath the R. stylosa pristine area during the wet season, and Operational Functional Unit (OFU) 1 was detected in all sediment samples representing 51 to 100% of the total number sequences in 70% of the samples. To study this functional biodiversity, a dye-decolorizing peroxidase-encoding (DyP) gene corresponding to OFU1 was selected and cloned in Pichia pastoris for heterologous expression. The recombinant enzyme, DyP1, was characterized concerning its physicochemical properties and ability to oxidize diverse phenolic substrates, together with its potential in decolorizing textile dyes. The optimal pH of DyP1 differed in relation to the substrates tested, and DyP1 was more active in acidic pH and stable in a rather large pH range. The enzyme has shown a very stable activity at temperatures up to 50 ?C, retaining 60 to 80% activity after 180 min of incubation at temperatures ranging from 30 to 70 ?C. A wide substrate specificity was observed with the lowest Km and highest catalytic efficiency values obtained against ABTS and Reactive blue 19, respectively. The industrial dyes Acid Black, Disperse blue 79 and Reactive Black 5 were decolorized with different percentages. Its activity related to salt was also studied and compared to other enzymes originating from marine-derived fungi.