Transcriptional analysis of genes for energy catabolism and hydrolytic enzymes in the filamentous fungus Aspergillus oryzae using cDNA microarrays and expressed sequence tags

Aspergillus oryzae is a fungus used extensively in the fermentation industry. We constructed cDNA microarrays comprising 2,070 highly expressed cDNAs selected from the approximately 6,000 non-redundant expressed sequence tags (ESTs) in the A. oryzae EST database (http://www.aist.go.jp/RIODB/ffdb/index.html). Using the cDNA microarrays, we analyzed the gene expression profiles of A. oryzae cells grown under the glucose-rich (AC) and glucose-depleted (AN) liquid culture conditions used during the construction of the EST database. The sets of genes identified by the cDNA microarray as highly expressed under each culture condition agreed well with the highly redundant ESTs obtained under the same conditions. In particular, transcription levels of most catabolic genes of the glycolytic pathway (EMP) and tricarboxylic acid (TCA) cycle were higher under AC than AN conditions, suggesting that A. oryzae uses both EMP and TCA for glucose metabolism under AC conditions. We further studied the expression of genes encoding hydrolytic enzymes and enzymes involved in energy catabolism by using three industrial solid-phase biomass media, including wheat-bran. The wheat-bran culture gave the richest gene expression profile of hydrolytic enzymes and the lowest expression levels of catabolic genes (EMP, TCA) among the three media tested. The low expression levels of catabolic genes in the wheat-bran culture may release catabolite repression, consequently leading to the rich expression profiles of the hydrolytic enzymes.