High resolution visualization and exo‐proteomics reveal the physiological role of XlnR and AraR in plant biomass colonization and degradation by Aspergillus niger

Abstract

In A. niger, two transcription factors, AraR and XlnR, regulate the production of enzymes involved in degradation of arabinoxylan and catabolism of the released l-arabinose and d-xylose. Deletion of both araR and xlnR in leads to reduced production of (hemi)cellulolytic enzymes and reduced growth on arabinan, arabinogalactan and xylan. In this study, we investigated the colonization and degradation of wheat bran by the A. niger reference strain CBS 137562 and araR/xlnR regulatory mutants using high-resolution microscopy and exo-proteomics. We discovered that wheat bran flakes have a 'rough' and 'smooth' surface with substantially different affinity towards fungal hyphae. While colonization of the rough side was possible for all strains, the xlnR mutants struggled to survive on the smooth side of the wheat bran particles after 20 and 40 h post inoculation. Impaired colonization ability of the smooth surface of wheat bran was linked to reduced potential of ΔxlnR to secrete arabinoxylan and cellulose-degrading enzymes and indicates that XlnR is the major regulator that drives colonization of wheat bran in A. niger.

Blocking utilization of major plant biomass polysaccharides leads Aspergillusniger towards utilization of minor components

“…The phenotype and exoproteome of the A. niger Δ xlnR mutant confirmed previous studies that reported impaired growth on cellulose, (arabino)xylan and xyloglucan (van Peij et al ., 1998a; Gruben et al ., 2017). Enzyme activity assays and proteomic studies also demonstrate the key role of XlnR in the utilization of (arabino)xylan and cellulose when grown on wheat bran, and correlate with a previous study that showed that colonization of wheat bran is mainly dependent on XlnR (Kowalczyk et al ., 2017a). However, it cannot be excluded that the phenotype of Δ xlnR includes reduced production of ClrA and ClrB targets, as it has previously been shown that XlnR affects the expression of the genes encoding these two transcription factors (Raulo et al ., 2016).…”

Dichomitus squalens partially tailors its molecular responses to the composition of solid wood

“…The digestion was quenched with a solution of trifluoroacetic acid (1%) before flash freezing and storing at −80°C. The salts and detergents were removed using SCX SPE as described in Kowalczyk and colleagues () and the final peptide concentration was determined using a BCA assay to ensure the samples were diluted to 0.1 μg·μl −1 for LC–MS/MS processing.…”

From lignocellulose to plastics: Knowledge transfer on the degradation approaches by fungi

“…the development of helium ion microscopy (HIM) led to an increase in imaging resolution and depth of field compared to scanning electron microscopy (SEM) (Joens et al, 2013). Using HIM, it was shown how A. niger hyphae colonised better on the "rough" compared to on the "smooth" surface of wheat bran (Kowalczyk et al, 2017). Also, HIM visualised the progressive degradation of lignocellulose over time, such as the thinning of cell wall structures in wood colonised by the white-rot D. squalens (Daly et al, 2018).…”