Department of Bioengineering, Gebze Technical University, Gebze, Kocaeli, Turkey.
IBSB, Department of Bioengineering, Marmara University, Istanbul, Turkey.
Appl Microbiol Biotechnol. 2019 Apr;103(7):3153-3165. doi: 10.1007/s00253-019-09630-4. Epub 2019 Feb 2.
Leuconostoc mesenteroides subsp. cremoris is an obligate heterolactic fermentative lactic acid bacterium that is mostly used in industrial dairy fermentations. The phosphoketolase pathway (PKP) is a unique feature of the obligate heterolactic fermentation, which leads to the production of lactate, ethanol, and/or acetate, and the final product profile of PKP highly depends on the energetics and redox state of the organism. Another characteristic of the L. mesenteroides subsp. cremoris is the production of aroma compounds in dairy fermentation, such as in cheese production, through the utilization of citrate. Considering its importance in dairy fermentation, a detailed metabolic characterization of the organism is necessary for its more efficient use in the industry. To this aim, a genome-scale metabolic model of dairy-origin L. mesenteroides subsp. cremoris ATCC 19254 (iLM.c559) was reconstructed to explain the energetics and redox state mechanisms of the organism in full detail. The model includes 559 genes governing 1088 reactions between 1129 metabolites, and the reactions cover citrate utilization and citrate-related flavor metabolism. The model was validated by simulating co-metabolism of glucose and citrate and comparing the in silico results to our experimental results. Model simulations further showed that, in co-metabolism of citrate and glucose, no flavor compounds were produced when citrate could stimulate the formation of biomass. Significant amounts of flavor metabolites (e.g., diacetyl and acetoin) were only produced when citrate could not enhance growth, which suggests that flavor formation only occurs under carbon and ATP excess. The effects of aerobic conditions and different carbon sources on product profiles and growth were also investigated using the reconstructed model. The analyses provided further insights for the growth stimulation and flavor formation mechanisms of the organism.
乳脂明串珠菌是一种必需的异型乳酸发酵乳酸菌，主要用于工业乳制品发酵。磷酸酮解酶途径（PKP）是异型乳酸发酵的一个独特特征，导致乳酸、乙醇和/或乙酸的产生，PKP 的最终产物谱高度依赖于生物体的能量学和氧化还原状态。乳脂明串珠菌的另一个特点是在乳制品发酵中产生香气化合物，如在奶酪生产中，通过利用柠檬酸盐。考虑到其在乳制品发酵中的重要性，对该生物体进行详细的代谢特征分析对于其在工业中的更有效利用是必要的。为此，构建了源自乳制品的乳脂明串珠菌 ATCC 19254（iLM.c559）的基因组规模代谢模型，以详细解释该生物体的能量学和氧化还原状态机制。该模型包含 559 个基因，控制 1088 个反应，涉及 1129 种代谢物，反应涵盖了柠檬酸盐的利用和与柠檬酸盐相关的风味代谢。通过模拟葡萄糖和柠檬酸盐的共代谢并将计算结果与实验结果进行比较，对模型进行了验证。模型模拟进一步表明，在柠檬酸盐和葡萄糖的共代谢中，当柠檬酸盐能够刺激生物量形成时，不会产生风味化合物。只有当柠檬酸盐不能促进生长时，才会产生大量的风味代谢物（例如，双乙酰和乙酰基），这表明只有在碳和 ATP 过剩的情况下才会发生风味形成。还使用重建的模型研究了好氧条件和不同碳源对产物谱和生长的影响。这些分析为该生物体的生长刺激和风味形成机制提供了进一步的见解。
