Metabolic engineering reveals the relative importance of different sugar catabolic pathways during consumption of plant biomass by Aspergillus niger

To evaluate the impact of individual sugar catabolic pathways on the physiology of A. niger when using plant biomass as a carbon source, key pathways converting plant biomass derived monomers were blocked. The resulting deletion mutants were analyzed using wheat bran and sugar beet pulp as substrates. On both substrates, the strongest affected single-pathway mutants were the pentose catabolic pathway (PCP) (ΔxkiA) and glycolysis (ΔhxkAΔglkA) deficient mutants. On wheat bran, which is rich in pentose sugars, blocking the PCP by deletion of xkiA strongly impacted both growth and gene expression. However, the effect was even stronger in ΔhxkAΔglkA and similar to a strain in which all pathways were blocked, highlighting the crucial role of glycolysis and/or carbon catabolite repression in A. niger physiology. These results demonstrate the complexity of A. niger metabolism during growth on plant biomass and provide insights into aspects to consider during metabolic engineering to obtain fungal cell factories.