Top Institute Food and Nutrition (TIFN), 6709 PA, Wageningen, The Netherlands.
Appl Microbiol Biotechnol. 2013 Oct;97(19):8729-39. doi: 10.1007/s00253-013-5140-2. Epub 2013 Aug 24.
Lactococcus lactis subsp. cremoris MG1363 is a paradigm strain for lactococci used in industrial dairy fermentations. However, despite of its importance for process development, no genome-scale metabolic model has been reported thus far. Moreover, current models for other lactococci only focus on growth and sugar degradation. A metabolic model that includes nitrogen metabolism and flavor-forming pathways is instrumental for the understanding and designing new industrial applications of these lactic acid bacteria. A genome-scale, constraint-based model of the metabolism and transport in L. lactis MG1363, accounting for 518 genes, 754 reactions, and 650 metabolites, was developed and experimentally validated. Fifty-nine reactions are directly or indirectly involved in flavor formation. Flux Balance Analysis and Flux Variability Analysis were used to investigate flux distributions within the whole metabolic network. Anaerobic carbon-limited continuous cultures were used for estimating the energetic parameters. A thorough model-driven analysis showing a highly flexible nitrogen metabolism, e.g., branched-chain amino acid catabolism which coupled with the redox balance, is pivotal for the prediction of the formation of different flavor compounds. Furthermore, the model predicted the formation of volatile sulfur compounds as a result of the fermentation. These products were subsequently identified in the experimental fermentations carried out. Thus, the genome-scale metabolic model couples the carbon and nitrogen metabolism in L. lactis MG1363 with complete known catabolic pathways leading to flavor formation. The model provided valuable insights into the metabolic networks underlying flavor formation and has the potential to contribute to new developments in dairy industries and cheese-flavor research.
乳球菌乳亚种 MG1363 是用于工业乳制品发酵的乳球菌的典型菌株。然而，尽管它对工艺开发很重要，但迄今为止尚未报道其基因组规模的代谢模型。此外，目前针对其他乳球菌的模型仅关注生长和糖降解。包含氮代谢和风味形成途径的代谢模型对于理解和设计这些乳酸菌的新工业应用至关重要。开发并实验验证了乳球菌 MG1363 的代谢和运输的基因组规模、基于约束的模型，该模型考虑了 518 个基因、754 个反应和 650 个代谢物。59 个反应直接或间接地参与风味形成。通量平衡分析和通量可变性分析用于研究整个代谢网络中的通量分布。厌氧碳限制连续培养用于估计能量参数。彻底的模型驱动分析显示了高度灵活的氮代谢，例如支链氨基酸代谢与氧化还原平衡相耦合，对于预测不同风味化合物的形成至关重要。此外，该模型预测了发酵过程中挥发性硫化合物的形成。随后在进行的实验发酵中鉴定出了这些产物。因此，基因组规模的代谢模型将乳球菌 MG1363 的碳氮代谢与完整的已知分解代谢途径相结合，从而导致风味形成。该模型为风味形成的代谢网络提供了有价值的见解，并有可能为乳制品行业和奶酪风味研究的新发展做出贡献。
