Abstract:Seven α-glucosidase genes have been annotated in the genome of Aspergillus niger CBS513.88, but the gene with predominant α-glucosidase activity has not been reported. A set of seven α-glucosidase-gene-knockout mutant strains of A. niger SH-2 were constructed by homologous recombination, with deletion of α-glucosidase genes B, A, E, G, C, D, and F. Measurement of α-glucosidase activity showed that in the agdB disruption mutant strain (ΔagdB) activity was decreased by 36% compared with that of the control strain, but there was no significant decrease with the other deletion mutants. Using the A. niger SH-2-3 strain with glucoamylase and amylase gene deletions as the host, and the agdA gene, that shows the highest identity with the reported α-glucosidase gene sequence from A. niger, and agdB were knocked out and overexpressed, respectively. The results showed that the growth rate of agdB disruption mutant strains was the slowest in culture medium without glucose, and increased with increasing glucose concentrations. The α-glucosidase activity in the agdB overexpressing strain (3-agdB) was ten times as much as that of the SH-2 wild-type strain. Therefore, the results of this study suggest that agdB is the gene with predominant α-glucosidase activity (36% of all α-glucosidase activity) among the seven predicted α-glucosidase genes in the A. niger SH-2 genome, but further investigation is required.
