To provide a spore-forming microorganism having a spore-forming ability at ordinary temperatures used for liquid cultivation for obtaining a starter for Bacillus natto and a temperature sensitive To provide natto with little Bacillus natto spore content by acquiring Bacillus subtilis natto and using the bacillus natto without problems such as inferior fermentation and bacterial contamination and existing facilities and processes.SOLUTION: Bacillus subtilis var. Natto mutant having the following properties (A) to (C), natto produced using the mutant strain, and natto using the mutant strain Thereby providing a manufacturing method. (A) The property of forming colonies on LB agar medium containing 5 g / ml of kanamycin or a salt thereof, after culturing at a gas phase temperature of 37 C. for 18 hours. (B) In the sporulation medium, when culturing the medium at a liquid temperature of 37 C., the number of spores of the Bacillus natto mutant is 1 107Characteristics to be more than 1 / ml. (C) The Natto bacterial mutant strain is added to boiled soybean or steamed soybean per gram of Bacillus natto spores 5 103When the temperature of the bean was kept in the range of 40 to 53 C., the stringiness and the characteristic aroma peculiar to natto were good, and the number of Bacillus natto spores per 5 g of natto was 5 105Nature capable of manufacturing natto or less.Selection drawing None【課題】植菌用の納豆菌スターター取得のための液体培養に通常用いられる温度帯では通常の胞子形成能を有するが、納豆発酵に通常用いられる温度帯では胞子形成能の低下した温度感受性の納豆菌を取得すること、及び当該納豆菌を用いて発酵不良や雑菌汚染といった問題がなく、既存の設備及び工程によって、納豆菌胞子の含有量が少ない納豆を提供すること。【解決手段】以下の(A)~(C)の性質を有する納豆菌(Bacillus subtilis var. natto)変異株、ならびに当該変異株を用いて製造された納豆、及び、当該変異株を用いる納豆の製造方法を提供する。 (A) 5μg/mlのカナマイシン又はその塩を含有するLB寒天培地において、気相温度37℃で18時間培養後にコロニーを形成する性質。 (B) 胞子形成培地において、培地の液温37℃で培養した際に、前記納豆菌変異株の胞子数が1×107個/ml以上となる性質。 (C) 前記納豆菌変異株を、煮大豆又は蒸煮大豆に1gあたり納豆菌胞子数5×103個となるように植菌し、豆の品温を40~53℃の範囲に維持した際に、糸引き、納豆特有の香りが良好で、かつ納豆1gあたり納豆菌胞子数が5×105個以下の納豆を製造できる性質。【選択図】なし
