The Key to Acetate: Metabolic Fluxes of Acetic Acid Bacteria under Cocoa Pulp Fermentation-Simulating Conditions
The Key to Acetate: Metabolic Fluxes of Acetic Acid Bacteria under Cocoa Pulp Fermentation-Simulating Conditions
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DOI：
10.1128/aem.01048-14
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发表时间：
2014-08-01
影响因子：
4.4
通讯作者：
Wittmann, Christoph
中科院分区：
文献类型：
--
作者：
Adler, Philipp;Frey, Lasse Jannis;Wittmann, Christoph
醋酸菌（AAB）在可可发酵过程中发挥着重要作用，因为其主要产物乙酸盐是开发所需可可风味的主要驱动力。在这里，我们研究了这些细菌的专门代谢可可浆发酵模拟条件下。一个精心设计的平行的C-13同位素标记实验的组合允许在可可浆的复杂环境中的细胞内通量的阐明，当乳酸盐和乙醇被包括在未定义的成分作为主要底物。我们证明，AAB表现出功能分离的代谢过程中的二碳和三碳底物的共同消费。乙酸盐几乎完全来自乙醇，而乳酸盐用于形成乙偶姻和生物质结构单元。虽然这对于细胞能量学来说是次优的，但这允许最大化生长和转化率。功能分离的结果是缺乏磷酸烯醇式丙酮酸羧激酶和苹果酸酶，通常存在于细菌互连代谢。事实上，异生是由丙酮酸磷酸二激酶驱动的。因此，乳酸盐和乙醇的平衡比例对于AAB的最佳性能是重要的。由于乳酸盐和乙醇在可可发酵的初始阶段分别由乳酸菌和酵母单独提供，这强调了良好平衡的微生物聚生体对于成功发酵过程的重要性。事实上，当乳酸菌和酵母菌都存在时，AAB在混合培养实验中表现最好并产生最大量的乙酸盐。
Acetic acid bacteria (AAB) play an important role during cocoa fermentation, as their main product, acetate, is a major driver for the development of the desired cocoa flavors. Here, we investigated the specialized metabolism of these bacteria under cocoa pulp fermentation-simulating conditions. A carefully designed combination of parallel C-13 isotope labeling experiments allowed the elucidation of intracellular fluxes in the complex environment of cocoa pulp, when lactate and ethanol were included as primary substrates among undefined ingredients. We demonstrate that AAB exhibit a functionally separated metabolism during coconsumption of two-carbon and three-carbon substrates. Acetate is almost exclusively derived from ethanol, while lactate serves for the formation of acetoin and biomass building blocks. Although this is suboptimal for cellular energetics, this allows maximized growth and conversion rates. The functional separation results from a lack of phosphoenolpyruvate carboxykinase and malic enzymes, typically present in bacteria to interconnect metabolism. In fact, gluconeogenesis is driven by pyruvate phosphate dikinase. Consequently, a balanced ratio of lactate and ethanol is important for the optimum performance of AAB. As lactate and ethanol are individually supplied by lactic acid bacteria and yeasts during the initial phase of cocoa fermentation, respectively, this underlines the importance of a well-balanced microbial consortium for a successful fermentation process. Indeed, AAB performed the best and produced the largest amounts of acetate in mixed culture experiments when lactic acid bacteria and yeasts were both present.