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Relative contribution of three transporters to D-xylose uptake in Aspergillus niger

Summary

Researchers studied how three different protein transporters help the fungus Aspergillus niger absorb xylose, a type of sugar found in plant waste. They found that two of these transporters (XltA and XltD) were equally important, while the third (XltB) played a minor role. Interestingly, the fungus could still absorb xylose even without these three transporters, suggesting other backup transporters exist. This finding shows that predicting which transporters are important based on laboratory tests in yeast may not accurately reflect how they work in the original fungus.

Background

D-xylose is the second most abundant sugar in lignocellulosic biomass and represents a promising substrate for biofuel and biochemical production. Efficient D-xylose uptake is essential for microbial utilization, making transporter optimization a key target for improving fungal cell factories. Three D-xylose transporters (XltA, XltB, XltD) have been identified in Aspergillus niger, a major industrial fungal host.

Objective

To evaluate the relative contribution of three D-xylose transporters (XltA, XltB, and XltD) to overall D-xylose uptake in Aspergillus niger at different sugar concentrations. The study aimed to determine whether kinetic characteristics and gene expression profiles correlate with transporter function in the native organism.

Results

XltA and XltD contributed similarly to D-xylose uptake (approximately 2.7-fold and 2.1-fold reduction when deleted), while XltB had minimal impact. Notably, D-xylose uptake persisted even in the triple deletion mutant, indicating involvement of additional transporters. No clear correlation was observed between the kinetic parameters determined in heterologous yeast expression systems and the actual physiological contribution of these transporters.

Conclusion

The study demonstrates that selection of transporters for metabolic engineering based solely on kinetic parameters from heterologous expression may not be reliable. XltA and XltD serve as major contributors to D-xylose uptake in A. niger, but the involvement of other uncharacterized transporters suggests a complex multi-transporter system for pentose uptake that warrants further investigation.
  • Published in:AIMS Microbiology,
  • Study Type:Experimental Research,
  • Source: 10.3934/microbiol.2025037, PMID: 41522442
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