Untargeted metabolic profiling of winery-derived biomass waste degradation by Aspergillus niger

BACKGROUND: Ascomycetes are capable of considerable lignocellulose degradation. However, there is limited knowledge on the metabolic profile of their biomass degradation. Metabolomic studies are capable of providing important biochemical information to understand and characterise fungal biomass degradation mechanisms. RESULTS: Winery biomass waste of Vitis vinifera var. Shiraz was subjected to Aspergillus niger mediated solid state fermentation for 8 days in 2H2O supplemented medium. Samples were collected every 24h, freeze-dried and derivatized before GC-MS analysis. Covariance-inverse multivariate statistics were used to classify the most significant metabolites. Metabolite-flux profiling classified 37 unique metabolites in 18 different pathways leading to or from glycolysis-tricarboxylic acid pathways. The majority of the sugars were consumed during the first 4 days; this was in order to synthesize fatty acids, amino acids and secondary metabolites. Inhibition started at day 5, as indicated by the accumulation of sugars and the plateauing of N-acetyl glucosamine (a major fungal cell wall component). CONCLUSIONS: A 4-day continuous yeast or mixed fungal fermentation will not only prevent product inhibition, but it will also aid in generating bio-ethanol. Inducing 2-keto-acid decarboxylases followed alcohol dehydrogenases at the onset of inhibition is predicted to aid in the generation of butanol isomers, which are considered valuable sources of fuel.