Re-routing central metabolism in Aspergillus nidulans

Plant biomass is the most abundant and renewable carbon source for many fungal species. The composition of biomass consists of about 40-45% cellulose, 20-30% hemicellulose, and 15-25% lignin and varies among plant species. In the bio-based industry, Aspergillus species and other fungi are used for the production of lignocellulolytic enzymes to pretreat agricultural waste biomass (e.g. wheat bran). In this study, we aimed to evaluate if it would be possible to create an Aspergillus strain that releases but does not metabolize hexoses from plant biomass. For this purpose, metabolic mutants were generated that were (partially) impaired in glycolysis, by deleting the hexokinase (hxkA) and glucokinase (glkA) genes. To prevent repression of enzyme production due to the accumulation of hexoses, strains were generated in which these mutations were combined with a mutation in creA, encoding the repressor involved in carbon catabolism. Phenotypic analysis revealed that growth of the ΔhxkAΔglkA mutant was reduced on wheat bran. However, hexoses did not accumulate during growth of the mutants on wheat bran, suggesting that glucose metabolism is re-routed towards alternative carbon catabolic pathways. Deletion of creA combined with blocking glycolysis resulted in an increased expression of pentose catabolic and phosphate pathway genes. This indicates that the reduced ability to use hexoses as carbon sources has resulted in a shift towards the pentose fraction of wheat bran as a major carbon source to support growth. This study compares the gene expression of several A. nidulans strains growing on MM + wheat bran. The different A. nidulans samples (wildtype, ΔhxkAΔglkA, ΔcreA, and ΔcreAΔhxkAΔglkA) were taken after 2 hours of incubation.