Transcriptome Analysis of Zones of Colonies of the ΔflbA Strain of Aspergillus niger

Abstract

Wild-type colonies of Aspergillus niger grow and secrete enzymes at their periphery when they are grown on an agar medium. Inactivation of the sporulation gene flbA results in colonies that not only secrete proteins at their periphery, but also in central zones. This is accompanied by a more complex secretome, growth throughout the mycelium, and by thinner cell walls. Here, gene expression was studied at the periphery, an intermediate zone, and the centre of wild-type and ΔflbA colonies using whole genome microarrays. Heterogeneity in gene expression was not reduced in ΔflbA colonies when compared to wild-type colonies, despite decreased heterogeneity in zonal secretion, sporulation and growth. It was shown that 1152 genes had a fold change difference in expression ≥ 2, when the averaged expression profiles of the zones of the wild-type were compared with those of ΔflbA colonies. This gene set contained 13 genes predicted to be involved in reproduction, 12 genes involved in cell wall biosynthesis, modification and degradation, 345 genes encoding secreted proteins and 38 genes encoding transcriptional regulators. These genes may account for the differences between wild-type and ΔflbA colonies in zonal growth, sporulation and secretion, and the complexity of the secretome and the thickness of the cell wall. The set of differentially expressed genes, in particular, the genes encoding transcriptional regulators, may be instrumental to improve Aspergillus niger as a cell factory for the production of enzymes