Abstract
Plant biomass is one of the main renewable materials on Earth. It is used as substrate by industry to convert it into useful products, such as biofuel and chemicals. Natural forests, forest plantations and agroforestry plantations are recognized as an important reservoir of renewable carbon. Fungi play an important role
... read more
in plant biomass degradation, also in forest ecosystems. Therefore, improving the production of fungal plant biomass converting enzymes is of great interest to biotechnology. These enzymes have been mainly studied in saprobic ascomycetes, and much less extensively in basidiomycetes. This is largely caused by the better manageability of ascomycetes in industrial fermentations and the availability of transformation systems for many ascomycetes, while these aspects are still a major challenge in basidiomycetes. Despite this, basidiomycetes form a promising source of novel enzymes with putatively different biochemical properties than ascomycete enzymes. Plant biomass consists mainly of polysaccharides, lignin and proteins, forming a complex network of polymers interacting with each other. White-rot basidiomycete fungi are well known for their unique ability to decompose all wood polymers, including the recalcitrant lignin, by secreting hydrolytic and oxidative enzymes. This ability has raised significant interest in white-rot fungi, since lignin removal from plant biomass remains a challenge in industry and academia. In this thesis, I focused on the white-rot fungus Dichomitus squalens as a basidiomycete model for plant biomass degradation, and extend those insights to other white-rot fungi. In the last years, the ability of this species to produce industrially relevant enzymes has been demonstrated, its genome encodes a broad range of enzymes for polysaccharide and lignin degradation, and its ligninolytic potential has been validated in both submerged and solid state cultures. This thesis focused on the genetical and physiological variation among different D. squalens strains in relation to plant biomass utilization and various approaches of the wood degradation process. For this, state of the art molecular and omics technologies were combined with amplified fragment length polymorphisms (AFLP), phylogeny, microscopy and enzyme activities, to demonstrate differences in the plant biomass degradation approach between mono- and dikaryotic strains, as well as between geographically different lineages of the fungus. It also revealed a partial adaptation of D. squalens to different wood types (hard- and softwood). In addition, I elucidated the response of D. squalens to the presence of mono- and oligomers derived from plant biomass and identified two inducers of CAZyme gene expression related to lignocellulose degradation. While these inducers were functional in both mono- and dikaryotic strains, their regulatory patterns showed differences between these strains.
show less
