Key Laboratory of Fermentation Engineering (Ministry of Education), Hubei University of Technology, Wuhan, 430068, China.
Appl Microbiol Biotechnol. 2013 Dec;97(23):9981-92. doi: 10.1007/s00253-013-5224-z. Epub 2013 Oct 5.
Tuber melanosporum, known as the black diamond of cuisine, is highly appreciated for its unique and characteristic aroma, which is mainly due to its volatile organic sulfur-containing compounds (VOSCs). In this work, by adding 5 g/L L-methionine to the fermentation medium, the activities of aminotransferase and α-ketoacid decarboxylase were significantly enhanced by 103 and 250%, respectively, while the activities of alcohol dehydrogenase and demethiolase were decreased by 277 and 39%. Then, the six VOSCs, i.e., methanethiol (MTL), dimethyl sulfide (DMS), dimethyl disulfide (DMDS), dimethyl trisulfide (DMTS), 3-(methylthio)propanal (methional), and 3-(methylthio)-1-propanol (methionol), were first detected in the submerged fermentation of T. melanosporum. These results indicated that the biosynthesis of VOSCs was triggered by aminotransferase and α-ketoacid decarboxylase. The production of methional and methionol increased with the increased concentrations of L-methionine (i.e., 5, 10, 15, and 20 g/L) before day 4 of the culture protocol, and methionol was the major product in the Ehrlich pathway. The production of MTL was significantly decreased after day 4 with a significantly increased DMDS, and DMDS was the major product of the demethiolation pathway. Compared with the demethiolation pathway with a total flux of sulfur of 11.33-24.32 μM, the Ehrlich pathway with a total flux of sulfur of 6,149-10,330 μM was considered the major pathway for the biosynthesis of VOSCs. This is the first report linking the metabolism of L-methionine to the biosynthesis of VOSCs by the Ehrlich and demethiolation pathways during the submerged fermentation of T. melanosporum.
块菌，俗称美食界的黑钻石，以其独特而典型的香气而备受推崇，其香气主要归因于挥发性含硫有机化合物（VOSCs）。在这项工作中，通过在发酵培养基中添加 5 g/L L-蛋氨酸，氨基转移酶和 α-酮酸脱羧酶的活性分别显著提高了 103%和 250%，而醇脱氢酶和脱巯基酶的活性分别降低了 277%和 39%。然后，在块菌的液体深层发酵中首次检测到 6 种 VOSCs，即甲硫醇（MTL）、二甲基硫（DMS）、二甲基二硫（DMDS）、二甲基三硫（DMTS）、3-（甲硫基）丙醛（甲硫醛）和 3-（甲硫基）-1-丙醇（甲硫醇）。这些结果表明，VOSCs 的生物合成是由氨基转移酶和 α-酮酸脱羧酶触发的。甲硫醛和甲硫醇的产量随着 L-蛋氨酸浓度的增加（即 5、10、15 和 20 g/L）而在培养方案的第 4 天之前增加，并且甲硫醇是 Ehrlich 途径的主要产物。第 4 天后，MTL 的产量显著下降，而 DMDS 显著增加，DMDS 是脱巯基途径的主要产物。与硫总通量为 11.33-24.32 μM 的脱巯基途径相比，硫总通量为 6,149-10,330 μM 的 Ehrlich 途径被认为是 VOSCs 生物合成的主要途径。这是首次报道在块菌的液体深层发酵过程中，L-蛋氨酸的代谢与 Ehrlich 和脱巯基途径的 VOSCs 生物合成有关。
