Overproduction of Glucoamylase by Recombinant Aspergillus niger Harboring Multiple Copies of glaA

The glucoamylase gene (glaA) of Aspergillus niger CICIM F0410 was cloned, sequenced, and expressed. The integrated plasmid pBC-Hygro-glaA carrying the glaA was constructed and transformed into A. niger F0410. Transformants with multiple copies of glaA integrated in the chromosome were selected by 150 μg/mL hygromycin B and identified by real-time PCR. Two to three multiples of glaA in the chromosome were found to be optimal for higher expression of glucoamylase. Shake-flask fermentation under optimal conditions showed that glucoamylase secreted by transformant GB0506 was 17.5% higher than that of parental strain F0410 at the end of fermentation. In conclusion, increasing copy numbers of glaA by chromosomal integration significantly improved the yield of glucoamylase in the industrial strain of A. niger.