Evidence for inducer function of 2-keto-3-deoxy-L-galactonate in D-galacturonic acid induced gene expression in Aspergillus niger. Aspergillus niger

In Aspergillus niger, the enzymes encoded by gaaA, gaaB, gaaC and gaaD catabolize D-galacturonic acid (GA) consecutively into L-galactonate, 2-keto-3-deoxy-L-galactonate, pyruvate and L-glyceraldehyde, and glycerol. We show here that deletion of gaaB or gaaC results in severely impaired growth on GA and accumulation of pathway intermediates L-galactonate and 2-keto-3-deoxy-L-galactonate, respectively. Expression levels of several GA-induced genes were specifically elevated in the ∆gaaC mutant on GA as compared to the reference strain or other GA catabolic pathway deletion mutants. The hyper-induction of GA-induced genes in ∆gaaC indicates that 2-keto-3-deoxy-L-galactonate is the inducer of genes required for GA utilization. Overall design: In this study, we constructed GA catabolic pathway deletion mutants (∆gaaA, ∆gaaB, ∆gaaC and ∆gaaD) to gain insight into regulation of GA-induced genes in A. niger. Comparative analysis of all the GA catabolic pathway deletion mutants indicates that 2-keto-3-deoxy-L-galactonate acts as the physiological inducer of the GA-induced genes. ----------------------------------------------------- This represents the ΔgaaC mutant only