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 <i>A. niger</i> 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) (Δ<i>xkiA</i>) and glycolysis (Δ<i>hxkA</i>Δ<i>glkA</i>) deficient mutants. On wheat bran, which is rich in pentose sugars, blocking the PCP by deletion of <i>xkiA</i> strongly impacted both growth and gene expression. However, the effect was even stronger in Δ<i>hxkA</i>Δ<i>glkA</i> and similar to a strain in which all pathways were blocked, highlighting the crucial role of glycolysis and/or carbon catabolite repression in <i>A. niger</i> physiology. These results demonstrate the complexity of <i>A. niger</i> metabolism during growth on plant biomass and provide insights into aspects to consider during metabolic engineering to obtain fungal cell factories.