Closely related fungi employ diverse enzymatic strategies to degrade plant biomass

Background Plant biomass is the major substrate for the production of biofuels and biochemicals, as well as food, textiles and other products. It is also the major carbon source for many fungi and enzymes of these fungi are essential for the depolymerization of plant polysaccharides in industrial processes. This is a highly complex process that involves a large number of extracellular enzymes as well as non-hydrolytic proteins, whose production in fungi is controlled by a set of transcriptional regulators. Aspergillus species form one of the best studied fungal genera in this field, and several species are used for the production of commercial enzyme cocktails. Results It is often assumed that related fungi use similar enzymatic approaches to degrade plant polysaccharides. In this study we have compared the genomic content and the enzymes produced by eight Aspergilli for the degradation of plant biomass. All tested Aspergilli have a similar genomic potential to degrade plant biomass, with the exception of A. clavatus that has a strongly reduced pectinolytic ability. Despite this similar genomic potential their approaches to degrade plant biomass differ markedly in the overall activities as well as the specific enzymes they employ. While many of the genes have orthologs in (nearly) all tested species, only very few of the corresponding enzymes are produced by all species during growth on wheat bran or sugar beet pulp. In addition, significant differences were observed between the enzyme sets produced on these feedstocks, largely correlating with their polysaccharide composition. Conclusions These data demonstrate that Aspergillus species and possibly also other related fungi employ significantly different approaches to degrade plant biomass. This makes sense from an ecological perspective where mixed populations of fungi together degrade plant biomass. The results of this study indicate that combining the approaches from different species could result in improved enzyme mixtures for industrial applications, in particular saccharification of plant biomass for biofuel production. Such an approach may result in a much better improvement of saccharification efficiency than adding specific enzymes to the mixture of a single fungus, which is currently the most common approach used in biotechnology.Peer reviewe

Similar is not the same : Differences in the function of the (hemi-)cellulolytic regulator XlnR (Xlr1/Xyr1) in filamentous fungi

The transcriptional activator XlnR (Xlr1/Xyr1) is a major regulator in fungal xylan and cellulose degradation as well as in the utilization of d-xylose via the pentose catabolic pathway. XlnR homologs are commonly found in filamentous ascomycetes and often assumed to have the same function in different fungi. However, a comparison of the saprobe Aspergillus niger and the plant pathogen Magnaporthe oryzae showed different phenotypes for deletion strains of XlnR. In this study wild type and xlnR/xlr1/xyr1 mutants of five fungi were compared: Fusarium graminearum, M. oryzae, Trichoderma reesei, A. niger and Aspergillus nidulans. Growth profiling on relevant substrates and a detailed analysis of the secretome as well as extracellular enzyme activities demonstrated a common role of this regulator in activating genes encoding the main xylanolytic enzymes. However, large differences were found in the set of genes that is controlled by XlnR in the different species, resulting in the production of different extracellular enzyme spectra by these fungi. This comparison emphasizes the functional diversity of a fine-tuned (hemi-)cellulolytic regulatory system in filamentous fungi, which might be related to the adaptation of fungi to their specific biotopes. Data are available via ProteomeXchange with identifier PXD001190

Additional file 2: of Closely related fungi employ diverse enzymatic strategies to degrade plant biomass

Combines Additional file Tables S2–S4 (excel format). Table S2A. Numbers of putative genes per CAZy family for the 10 genomes addressed in this study. Table S2B. Numbers of putative genes per Plant Polysaccharide Degradation-related CAZy family for the 10 genomes addressed in this study. Table S3A. Orthology clusters of feruloyl esterase (SF), glycoside hydrolase (GH), carbohydrate esterase and polysaccharide lyase (PL) families. Table S3B. Orthology clusters of auxiliary activities (AA). Table S4A. Detection of proteins in cultures grown on wheat bran sorted by CAZy family. Table S4B. Detection of proteins in cultures grown on sugar beet pulp sorted by CAZy family. Table S4C. Detected proteins in cultures grown on wheat bran sorted by number of species that contain an orthologue. Table S4D. Detected proteins in cultures grown on sugar beet pulp sorted by number of species that contain an orthologue

Additional file 1: of Closely related fungi employ diverse enzymatic strategies to degrade plant biomass

Combines Additional File Figures S1–S4 and Table S1. Figure S1: Hydrolytic enzyme activity profiles of the eight species. Figure S2: Laccase activity of the eight species. Figure S3: Differences in feruloyl esterase production. Figure S4: Conserved SDS-PAGE profiles for isolates of the same species. Table S1. Strains used in this study