Lignocellulose biorefineries seek the integral use of plant biomass to produce chemicals, fuels and materials. While technologies for carbohydrate conversion are well established, technologies for the processing and recovery of lignin are considerably less developed. Technical lignins obtained as by-products from paper pulp or cellulosic biofuel production are burned to generate energy and only a minimum percentage is marketed. However, the convertion of this fraction of the plant biomass into valuable products is crucial for the economic viability of lignocellulose biorefineries. Indeed, lignin is a large reservoir of aromatic compounds and can be an invaluable source of phenolic molecules to be used as platform chemicals or active aromatic ingredients, for which the development of new (bio)chemical processes for transformation of this polymer is mandatory.
Ligninolytic fungi and their oxidative enzymes are a good alternative to chemical methods in industrial processes where depolymerization of lignin is required. Among them, basidiomycetes of the order Polyporales, which include most species of wood rotters, have been exhaustively studied improving our basic knowledge on ligninolytic oxidoreductases. In addition, different studies have revealed that these enzymes may be the biocatalysts of choice for the delignification of plant biomass in the context of biorefinery. However, the scarcely studied saprotrophic basidiomycetes of the order Agaricales, can be also an important source of varied oxidoreductases with biotechnological potential due to the diversity of lifestyles. In fact, three ecophysiological groups are distinguished within these fungi, depending on the degraded lignocellulosic substrate (wood, litter or buried wood). Because of this knowledge gap, a genome sequencing project of thirty-two representative saprotrophic Agaricales was initiated in collaboration with the US Department of Energy of the Joint Genome Institute under our coordination.
The proposed GENOBIOREF project will focus on the exhaustive analysis of these and other genomes of Agaricales to study enzymatic systems acting on plant biomass. This genomic analysis will be complemented with secretomic studies of species representative of the three mentioned ecophysiological groups and their ligninolytic oxidoreductases (including peroxidases and laccases). Preeliminar comparison of Agaricales enzymes with typical ligninolytic oxidoreductases from Polyporales has suggested novel oxidoreductase families, whose subsequent characterization will shed light on the role of these groups of fungi in the carbon cycle and provide the basis to design new biocatalysts. First, a profound characterization of the novel enzymes (after heterologous expression and purification) will allow us to advance in the knowledge of peroxidases and laccases and to disclose the most promising ones to be used as biocatalysts. Subsequently, when necessary, enzyme stability and/or catalytic activity will be improved by directed evolution or rational design to adjust enzyme properties to the operating conditions, thus improving the efficiency of the biocatalyst. Finally, the new enzymes will be evaluated individually in oxidative cross-linking reactions for valorization of technical lignins, or as part of a minimal in vitro ligninolytic system (precisely designed during the project) for the depolymerization of lignin polymer into simple monomers.