Sirtuin SirD is involved in α-amylase activity and citric acid production in Aspergillus luchuensis mut. kawachii during a solid-state fermentation process.

Sirtuins are understood to play a significant role in growth phase-dependent gene expression. In the study presented here, we examined the sirtuins in the white koji fungus, Aspergillus luchuensis mut. kawachii (Aspergillus kawachii), to examine their role in the regulation of amylolytic enzymes and citric acid production during solid-state culture (koji). Characterization of rice koji made using five sirtuin gene disruptants indicated that these genes are involved in the amylolytic activity and acidity of rice koji; the sirD disruptant in particular showed lower levels of acid-stable α-amylase activity and citric acid production per mycelial weight in koji compared to the control strain. The sirD disruptant also showed a change in mycelial pigmentation, and had higher sensitivity to cell wall biogenesis inhibitors such as calcofluor white and Congo red and reduced conidia formation. These results indicate that SirD is required for secondary metabolism, cell wall integrity, and conidial development. Cap analysis gene expression (CAGE) and quantitative RT-PCR analysis indicated that transcriptional changes were related to the characteristic phenotype of the sirD disruptant, including a reduced transcript level of the acid-stable α-amylase gene and a citric acid exporter in rice koji. These results indicate that SirD has a significant role in global transcriptional regulation, including the production of acid-stable α-amylase and citric acid, in A. kawachii during the solid-state fermentation process.