C4-dicarboxylic acids, including malic acid, fumaric acid and succinic acid, are valuable organic acids that can be produced and secreted by a number of microorganisms. Aspergillus carbonarius is capable of producing high amounts of citric acid, however, all attempts to change the citric acid production into C4-dicarboxylic production by pathway engineering have been with very limited success. In this study, a glucose oxidase deficient strain of A. carbonarius was used as the parental strain to overexpress a native C4-dicarboxylate transporter and the frd gene encoding fumarate reductase from Trypanosoma brucei individually and in combination to investigate their impacts on organic acid production. Overexpression of the C4-dicarboxylate transporter alone and in combination with the frd gene significantly increased the production of C4-dicarboxylic acids and reduced the accumulation of citric acid, whereas expression of the frd gene alone did not result in any significant change of the organic acid production profile. This study demonstrates that the key to change the citric acid production into production of C4-dicarboxylic acids in A. carbonarius is the C4-dicarboxylate transporter. Furthermore it shows that the C4-dicarboxylic acid production in A. carbonarius can be further increased via metabolic engineering.
Full conference title:
- Asperfest 14 (2017)