火落ち菌は日本酒を酸敗させる乳酸菌であり,生育にメバロン酸を要求することが知られている.最近の乳酸菌の分類学では,これらの細菌はFructilactobacillus fructivoransとLactobacillus acetotoleransの菌株として分類されている.火落ち菌の性状を検討するために,F. fructivoransとL. acetotoleransの4株ずつについてメバロン酸と,分子内にオレイン酸を含むTween 80の要求性について調べた.F. fructivorans NBRC 15887株は以前,Lactobacillus homohiochiiと分類されていた株であるが,これまでに知られていたように生育にメバロン酸を要求した.しかし,他の株はメバロン酸の明瞭な要求性は示さなかった.Tween 80については,F.uctivorans NBRC 13118株とL. acetotoleransの3株が要求性を示した.F. fructivorans菌株におけるTween 80と菌体脂肪酸中のオレイン酸の関連性は明瞭ではなかったが,L. acetotolerans菌株をTween 80添加培地で培養した場合には,cis-バクセン酸(Δ11-C18:1)に対するオレイン酸の比率が顕著に増加した.Tween 80の有無に関係なくF. fructivorans3株の菌体脂肪酸中には長鎖脂肪酸(C20:0,C20:1,C22:0)が検出され,C20:1についてはピロリジン誘導体をGC-MS分析することでΔ13-エイコセン酸(Δ13-C20:1)と同定された.これらの長鎖脂肪酸はF. fructivorans NBRC 13118株とL. acetotolerans菌株では検出されなかった.これらのデータから,NBRC 13118株の分類学的位置については再検討するべきであると考えられた.

Hiochi-bacteria are the lactic acid bacteria that acidify and spoil Japanese Sake, and known to require mevalonic acid for their growth. By recent taxonomy of lactic acid bacteria, they are classified to strains of Fructilactobacillus fructivorans and Lactobacillus acetotolerans. In order to investigate the characteristics of hiochi-bacteria, four strains each of F. fructivorans and L. acetotolerans were analyzed for their requirement of mevalonic acid and Tween 80 which contains oleic acid (Δ9-C18:1) in the molecule. F. fructivorans NBRC 15887, formerly classified as Lactobacillus homohiochii, showed requirement of mevalonic acid for growth as known previously, but other strains did not show notable requirement of this acid. Tween 80 was required by F. fructivorans NBRC 13118 and three strains of L. acetotolerans. The correlation of Tween 80 and oleic acid in cellular fatty acids was not clear among F. fructivorans strains, but the ratio of oleic acid to cis-vaccenic acid (Δ11-C18:1) increased markedly when L. acetotolerans strains were cultured with the medium containing Tween 80. Independent of the addition of Tween 80, the long-chain fatty acids (C20:0, C20:1, and C22:0) were detected in the cellular fatty acids of three strains of F. fructivorans, and C20:1 was identified as Δ13-eicosenoic acid (Δ13-C20:1) by GC-MS analysis of its pyrrolidide derivative. These long-chain fatty acids were not detected in F. fructivorans NBRC 13118 and strains of L. acetotolerans. From these data, it is proposed that the strain NBRC 13118 should be reexamined for the taxonomical position.