Re-routing of Sugar Catabolism Provides a Better Insight Into Fungal Flexibility in Using Plant Biomass-Derived Monomers as Substrates

Abstract

The filamentous ascomycete Aspergillus niger has received increasing interest as a cell factory, being able to efficiently degrade plant cell wall polysaccharides as well as having an extensive metabolism to convert the released monosaccharides into value added compounds. The pentoses D-xylose and L-arabinose are the most abundant monosaccharides in plant biomass after the hexose D-glucose, being major constituents of xylan, pectin and xyloglucan. In this study, the influence of selected pentose catabolic pathway (PCP) deletion strains on growth on plant biomass and re-routing of sugar catabolism was addressed to gain a better understanding of the flexibility of this fungus in using plant biomass-derived monomers. The transcriptome, metabolome and proteome response of three PCP mutant strains, ΔlarAΔxyrAΔxyrB, ΔladAΔxdhAΔsdhA and ΔxkiA, grown on wheat bran (WB) and sugar beet pulp (SBP), was evaluated. Our results showed that despite the absolute impact of these PCP mutations on pure pentose sugars, they are not as critical for growth of A. niger on more complex biomass substrates, such as WB and SBP. However, significant phenotypic variation was observed between the two biomass substrates, but also between the different PCP mutants. This shows that the high sugar heterogeneity of these substrates in combination with the high complexity and adaptability of the fungal sugar metabolism allow for activation of alternative strategies to support growth.

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

“…proteins, metabolites) (Liaud et al ., 2015; Amores et al ., 2016). However, efficient design of such cell factories requires a detailed understanding of the plant biomass conversion process at the molecular level (Chroumpi et al ., 2021). Plant biomass conversion by fungi involves a complex system of transcriptional regulation to ensure that the right set of enzymes is produced that matches the composition of the prevailing substrate.…”

Genome Mining Reveals a Surprising Number of Sugar Reductases in Aspergillus niger

“…The PCR DNA and Gel Band Purification Kit (Promega, Leiden, The Netherlands) was used to purify the amplified swap cassettes. A. niger protoplasting was performed, as previously described [14]. Polyethylene glycol (PEG)-mediated transformation of A. niger protoplasts was performed, as described in detail in [25].…”

“…A previous study demonstrated that the first step in pentose catabolism, the conversion of D-xylose and L-arabinose into xylitol and L-arabitol, respectively, involves at least three pentose reductase enzymes in A. niger, the NADPHdependent L-arabinose reductase (LarA, NRRL3_10050; EC 1.1.1.21) [11] and two D-xylose reductases (XyrA, NRRL3_1952; XyrB, NRRL3_10868; EC 1.1.1.307) [12,13]. The triple deletion mutant of these genes [14] did not significantly reduce the growth of A. niger on wheat bran (WB) and sugar beet pulp (SBP), which contain considerable amounts of L-arabinose and D-xylose. This may be due to the presence of other components in these substrates but could also indicate the involvement of additional genes that are expressed under these conditions but not during growth on L-arabinose or D-xylose.…”

The Sugar Metabolic Model of Aspergillus niger Can Only Be Reliably Transferred to Fungi of Its Phylum

“…Metabolomics analysis of intracellular metabolites was performed as previously described [42]. Briefly, metabolites were extracted from the ground mycelia underwent methoximation and silylation with N-methyl-N-trimethylsilyltrifluoroacetamide and 1% trimethylchlorosilane (MSTFA).…”