This thesis aims to determine the physiological role of D-xylose transporters in Aspergillus niger and their impact on sugar uptake efficiency. The study compares the fermentation profiles of a wild-type strain against mutant strains with transporter gene deletions under low and high xylose concentrations. At the low concentration, the mutant strains displayed a significant delay in substrate depletion compared to the wild type, indicating that missing transporters are crucial for high-affinity uptake. Under high conditions, the wild type exhibited a rapid acceleration uptake after 24 hours, whereas the mutants followed a slower, linear consumption pattern. Despite these delays, the mutant strains were eventually able to fully consume the xylose, suggesting the presence of alternative, unidentified transport pathways. The results conclude that while Aspergillus niger possesses redundant systems, the specific transporters studied are essential for optimizing fermentation speed and handling varying substrate levels.