CreA modulates the XlnR-induced expression on xylose of Aspergillus niger genes involved in xylan degradation

The expression of the feruloyl esterase gene faeA, the alpha-glucuronidase gene aguA, the endo-xylanase gene xlnB, and the beta-xylosidase gene xlnD f rom Aspergillus niger on xylose was studied in a wild-type strain and in a CreA mutant. A decrease in expression of all four genes was observed with i ncreasing xylose concentrations in the wild-type strain, whereas expression levels in the CreA mutant were not influenced. The results in the wild typ e indicated that xylose concentrations higher than 1 mM resulted in repress ion of the expression of the xylanolytic genes tested mediated by the carbo n catabolite repressor protein CreA. On xylose, the expression levels of th e xylanolytic genes were therefore not only determined by induction via Xln R, but also by repression via CreA. The genes tested were not influenced to the same extent by XlnR or CreA, resulting in specific expression levels a nd patterns for each individual gene. (C) Elsevier, Paris.