Futagami Taiki, Mori Kazuki, Wada Shotaro, Ida Hiroko, Kajiwara Yasuhiro, Takashita Hideharu, Tashiro Kosuke, Yamada Osamu, Omori Toshiro, Kuhara Satoru, Goto Masatoshi
Appl Environ Microbiol. 2015 Feb;81(4):1353-63. doi: 10.1128/AEM.03483-14.
The koji mold Aspergillus kawachii is used for making the Japanese distilled spirit shochu. During shochu production, A. kawachii is grown in solid-state culture (koji) on steamed grains, such as rice or barley, to convert the grain starch to glucose and produce citric acid. During this process, the cultivation temperature of A. kawachii is gradually increased to 40 °C and is then lowered to 30 °C. This temperature modulation is important for stimulating amylase activity and the accumulation of citric acid. However, the effects of temperature on A. kawachii at the gene expression level have not been elucidated. In this study, we investigated the effect of solid-state cultivation temperature on gene expression for A. kawachii grown on barley. The results of DNA microarray and gene ontology analyses showed that the expression of genes involved in the glycerol, trehalose, and pentose phosphate metabolic pathways, which function downstream of glycolysis, was downregulated by shifting the cultivation temperature from 40 to 30 °C. In addition, significantly reduced expression of genes related to heat shock responses and increased expression of genes related with amino acid transport were also observed. These results suggest that solid-state cultivation at 40 °C is stressful for A. kawachii and that heat adaptation leads to reduced citric acid accumulation through activation of pathways branching from glycolysis. The gene expression profile of A. kawachii elucidated in this study is expected to contribute to the understanding of gene regulation during koji production and optimization of the industrially desirable characteristics of A. kawachii.
米曲霉用于酿造日本蒸馏酒烧酒。在烧酒生产过程中，米曲霉在固态培养（曲）中生长于蒸煮过的谷物（如大米或大麦）上，将谷物淀粉转化为葡萄糖并产生柠檬酸。在此过程中，米曲霉的培养温度逐渐升至40℃，然后降至30℃。这种温度调节对于刺激淀粉酶活性和柠檬酸积累很重要。然而，温度对米曲霉基因表达水平的影响尚未阐明。在本研究中，我们调查了固态培养温度对在大麦上生长的米曲霉基因表达的影响。DNA微阵列和基因本体分析结果表明，将培养温度从40℃转变为30℃会下调参与糖酵解下游功能的甘油、海藻糖和磷酸戊糖代谢途径相关基因的表达。此外，还观察到热休克反应相关基因的表达显著降低，以及氨基酸转运相关基因的表达增加。这些结果表明，40℃的固态培养对米曲霉有压力，热适应通过激活糖酵解分支途径导致柠檬酸积累减少。本研究阐明的米曲霉基因表达谱有望有助于理解制曲过程中的基因调控以及优化米曲霉的工业理想特性。
