In this thesis, I explored how deleting the aoxA and aoxB genes affects citric acid production in Aspergillus niger. By comparing the double knockout strain to the wild type, I was able to clearly see how the absence of the AOX pathway shifts metabolism from citric acid formation toward biomass growth. My results showed that the mutant grew faster but produced significantly less citric acid, highlighting the important role of AOX in maintaining redox balance during fermentation. I also confirmed that morphology remained unchanged, meaning the differences came purely from metabolic regulation. Overall, this work helped me better understand how mitochondrial pathways influence industrial production and how manipulating AOX can impact the efficiency of citric acid fermentation.