Study of the glucoamylase promoter in Aspergillus niger using green fluorescent protein.

An Aspergillus niger strain expressing a red-shifted green fluorescent protein (GFP) in the cytoplasm under the control of the glucoamylase promoter (PgIaA) was characterized with respect to its physiology and morphology. Although xylose acted as a repressor carbon source during batch cultivations, PgIaA-driven GFP expression by the glucoamylase promoter could be demonstrated in xylose-limited continuous cultures. In these cultivations, the xylose concentration was therefore too low to cause repression. Transient experiments initiated with a maltose pulse did not further induce red-shifted GFP production in xylose-limited continuous cultures. Maltose induction under conditions of xylose repression was microscopically observed and quantified in a flow-through chamber. Red-shifted GFP was first produced after 5 h induction. Finally the strain was characterized in glucose-limited continuous cultures, and here the area of the mycelium stained with cytoplasmic GFP increased with increasing specific growth rate, indicating that GFP can be used as a marker of cellular activity in this type of cultivation.