The filamentous fungus Aspergillus niger is widely used in industry for the production of enzymes and organic acids. The reason for the widespread use of this fungus lies in its ability to produce high amounts of extracellular enzymes and primary metabolites. However, the fungus also produces a considerable amount of unwanted by-products such as polyols and a mixture of organic acids. The by-product formation is problematic both in relation to downstream processing and fermentation process efficiency.

A. niger has been studied for many years and extensive knowledge of central enzymes and pathways has been generated. Even though processes have been improved substantially there is still room for gaining additional information about the metabolism of the organism both regarding the evolutionary rationale or metabolic constraints leading to both product (in the case of organic acids) and by-product formation and strategies for rational engineering of metabolism.

Furthermore, the processes employed by industry are in many cases not well described in literature making it difficult for researchers to direct their efforts towards phenomena relevant to the industrial reality. This project aims at providing systems wide information about the metabolism during oxygen limited fed-batch fermentations resembling the industrial process for glucoamylase production. To this end laboratory scale fed-batch fermentations at several different conditions will be subjected to microarray analysis and vigorous characterization with regard to all compounds relevant to the carbon balance and this data will be combined with a genome wide metabolic model to yield a detailed picture of metabolism useful in designing better processes and strains.

Fed-batch fermentations investigating the impact of glucose concentration/feed control on process performance has been carried out. These fermentations show that by lowering the glucose concentration the production of most by-products is lowered. This is not only true for glycerol known to be involved in osmo-regulation, but also for other metabolites. D-mannitol is an exception as it is produced in slightly higher amounts.

Furthermore, an improved HPLC method revealed new and interesting aspects of the by-product spectrum regarding the identity of key metabolites. Identification and quantification of these compounds are on-going.

The project is financed by The Novozymes Bioprocess Academy.

Extended Abstract Status: Not Uploaded