Production and characterization of novel lignin-modifying enzymes from actinomycetes and heterologous expression of metagenome-source laccases. Produzione e caratterizzazione di enzimi ligninolitici in attinomiceti e espressione eterologa di laccasi da metagenoma.

The lignin is a recalcitrant aromatic biopolymer and its bio-degradation occurs by white rot fungi through the production of an enzyme array such as lignin, manganese and versatile peroxidases and laccases. The aims of this PhD project were the production and characterization of novel lignin-degrading enzymes from actinomycetes and the heterologous expression of a metagenome-sourced laccase. The classical approach of screening applied to microbial isolates led to the discovery of a novel peroxidase activity produced by Nonomuraea gerenzanensis. This peroxidase showed features such as high alkaline pH, thermo stability and decolorization of industrial dyes that favorably compare with the ones of fungal peroxidases. A possible application for this peroxidase might be in textile and decontamination meal of environmental pollutants. The metagenome-based approach allows to overcome cultivation-dependent limitations, directly analyzing genomes’ potential in environmental samples. This approach led to the discovery of a novel bacterial laccase (MetaLacc) affiliated to phylum Acidobacteria. MetaLacc shows ability to oxide a variety of phenolic substrates in a wide range of pHs, high tolerance towards salts, increased activity in the presence of alcohols and decolorization of industrial dyes. A possible application for Metalac might be as well in the treatment industrial wastewater. Finally, N. gerenzanensis and Streptomyces coelicolor A3 (2) were analyzed to degrade wheat straw or/and lignin in a two-stage bioconversion process. The first stage is the enzymatic digestion of pre-treated wheat straw by the two selected aerobic microorganisms. A second stage of anaerobic fermentation to produce biofuels will eventually follow.