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

Correspondence with D. McKie

December 1935 - November 1944. 11 letter

Overexpression, purification and characterisation of homologous α-L-arabinofuranosidase and endo-1,4-β-D-glucanase in Aspergillus vadensis

In the recent past, much research has been applied to the development of Aspergillus, most notably A. niger and A. oryzae, as hosts for recombinant protein production. In this study, the potential of another species, Aspergillus vadensis, was examined. The full length gDNA encoding two plant biomass degrading enzymes, i.e. α-L-arabinofuranosidase (abfB) (GH54) and endo-1,4-β-D-glucanase (eglA) (GH12) from A. vadensis were successfully expressed using the gpdA promoter from A. vadensis. Both enzymes were produced extracellularly in A. vadensis as soluble proteins and successfully purified by affinity chromatography. The effect of culture conditions on the expression of abfB in A. vadensis was examined and optimised to give a yield of 30 mg/L when grown on a complex carbon source such as wheat bran. Characterization of the purified α-L-arabinofuranosidase from A. vadensis showed an optimum pH and temperature of pH 3.5 and 60 °C which concur with those previously reported for A. niger AbfB. Comparative analysis to A. niger AbfA demonstrated interesting differences in temperate optima, pH stability and substrate specificities. The endo-1,4-β-D-glucanase from A. vadensis exhibited a pH and temperature optimum of pH 4.5 and 50 °C, respectively. Comparative biochemical analysis to the orthologous EglA from A. niger presented similar pH and substrate specificity profiles. However, significant differences in temperature optima and stability were noted

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

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