Tuesday, April 30, 2013
Exhibit Hall
The filamentous fungus Aspergillus carbonarius was identified as a good natural biocatalyst for production of organic acids through a screening program and is selected for pathway engineering. This includes engineering of the central carbon metabolism to improve the conversion of the renewable carbon sources and the flux into selected organic acids. The present work focuses on development of two different mutants, a gox mutant and a pepck mutant. The gox mutant was constructed by deleting the gox gene, which is assumed to encode the glucose oxidase in A. carbonarius, as there is a very high accumulation of gluconic acid as the main byproduct during organic acid fermentation from glucose. It was shown that the glucose consumption and efficiency of citric acid production were improved compared with the wildtype strain, and no gluconic acid could be detected from gox mutants. The pepck mutant was constructed by inserting the gene pepck, which encodes the phosphoenolpyruvate carboxykinase in Actinobacillus succinogenes, into A. carbonarius, in order to create a new bypass for shunting the carbon flux into the reductive pathway for stimulating the organic acid production. An improvement on both malic acid and citric acid production was observed which may result from the competition on the phosphoenolpyruvate with the original pathway. This may further lead to the enhanced carbon flux towards the cytosolic reductive pathway. Combining the two mutations in one strain shall demonstrate whether the production of organic acids will further increase.