In order to improve the production of succinate and malate by the filamentous fungus Aspergillus niger the activity of the glyoxylate bypass pathway was increased by over-expression of the isocitrate lyase (icl) gene. The hypothesis was that when isocitrate lyase was up-regulated the flux towards glyoxylate would increase, leading to excess formation of malate and succinate compared to the wild-type. However, metabolic network analysis showed that an increased icl expression did not result in an increased glyoxylate bypass flux. The analysis did show a global response with respect to gene expression, leading to an increased flux through the oxidative part of the TCA cycle. Instead of an increased production of succinate and malate, a major increase in fumarate production was observed.

The effect of malonate, a competitive inhibitor of succinate dehydrogenase (SDH), on the physiological behaviour of the cells was investigated. Inhibition of SDH was expected to lead to succinate production, but this was not observed. There was an increase in citrate and oxalate production in the wild-type strain. Furthermore, in the strain with over-expression of icl the organic acid production shifted from fumarate towards malate production when malonate was added to the cultivation medium.

Overall, the icl over-expression and malonate addition had a significant impact on metabolism and on organic acid production profiles. Although the expected succinate and malate formation was not observed, a distinct and interesting production of fumarate and malate was found.

为了改善丝状真菌黑曲霉的琥珀酸和苹果酸的生产，通过过表达异柠檬酸裂合酶（icl）基因来增加乙醛酸旁路途径的活性。假设是，当异柠檬酸裂合酶上调时，通向乙醛酸的通量将增加，与野生型相比，导致苹果酸和琥珀酸的过量形成。但是，代谢网络分析显示icl升高表达不导致乙醛酸旁路通量增加。该分析确实显示了对基因表达的整体响应，从而导致通过TCA循环氧化部分的通量增加。观察到富马酸酯产量显着增加，而不是琥珀酸和苹果酸的增加。

研究了丙二酸（一种琥珀酸脱氢酶（SDH）的竞争性抑制剂）对细胞生理行为的影响。预期SDH的抑制会导致琥珀酸的产生，但未观察到。野生型菌株中柠檬酸盐和草酸盐的产量增加。此外，在icl过表达的菌株中，当向培养基中添加丙二酸时，有机酸的生产从富马酸向苹果酸的生产转移。

总体而言，icl的过表达和丙二酸酯的添加对代谢和有机酸的产生具有重要影响。尽管未观察到预期的琥珀酸酯和苹果酸的形成，但发现了富马酸酯和苹果酸的独特而有趣的产物。