Azizan Kamalrul Azlan, Ressom Habtom W, Mendoza Eduardo R, Baharum Syarul Nataqain
Metabolomics Research Laboratory, Institute of Systems Biology (INBIOSIS), Universiti Kebangsaan Malaysia (UKM), Bangi, Selangor, Malaysia.
Departments of Oncology, Georgetown Lombardi Comprehensive Cancer Center, Georgetown University Medical Center, Washington, D.C., United States of America.
PeerJ. 2017 Jul 5;5:e3451. doi: 10.7717/peerj.3451. eCollection 2017.
subsp. MG1363 is an important starter culture for dairy fermentation. During industrial fermentations, is constantly exposed to stresses that affect the growth and performance of the bacterium. Although the response of to several stresses has been described, the adaptation mechanisms at the level of fluxes have seldom been described. To gain insights into cellular metabolism, C metabolic flux analysis and gas chromatography mass spectrometry (GC-MS) were used to measure the flux ratios of active pathways in the central metabolism of when subjected to three conditions varying in temperature (30°C, 37°C) and agitation (with and without agitation at 150 rpm). Collectively, the concentrations of proteinogenic amino acids (PAAs) and free fatty acids (FAAs) were compared, and Pearson correlation analysis () was calculated to measure the pairwise relationship between PAAs. Branched chain and aromatic amino acids, threonine, serine, lysine and histidine were correlated strongly, suggesting changes in flux regulation in glycolysis, the pentose phosphate (PP) pathway, malic enzyme and anaplerotic reaction catalysed by pyruvate carboxylase (pycA). Flux ratio analysis revealed that glucose was mainly converted by glycolysis, highlighting the stability of central carbon metabolism despite different conditions. Higher flux ratios through oxaloacetate (OAA) from pyruvate (PYR) reaction in all conditions suggested the activation of pyruvate carboxylate (pycA) in , in response to acid stress during exponential phase. Subsequently, more significant flux ratio differences were seen through the oxidative and non-oxidative pentose phosphate (PP) pathways, malic enzyme, and serine and C1 metabolism, suggesting NADPH requirements in response to environmental stimuli. These reactions could play an important role in optimization strategies for metabolic engineering in . Overall, the integration of systematic analysis of amino acids and flux ratio analysis provides a systems-level understanding of how regulates central metabolism under various conditions.
亚种MG1363是乳制品发酵的重要起始培养物。在工业发酵过程中，它不断受到影响细菌生长和性能的压力。尽管已经描述了该菌对几种压力的反应，但在通量水平上的适应机制却很少被描述。为了深入了解细胞代谢，采用碳代谢通量分析和气相色谱-质谱联用（GC-MS）技术，测量该菌在温度（30°C、37°C）和搅拌（150转/分搅拌和不搅拌）三种不同条件下中央代谢中活跃途径的通量比。同时，比较了蛋白质ogenic氨基酸（PAAs）和游离脂肪酸（FAAs）的浓度，并计算了Pearson相关分析（）以测量PAAs之间的成对关系。支链和芳香族氨基酸、苏氨酸、丝氨酸、赖氨酸和组氨酸相关性很强，这表明糖酵解、磷酸戊糖（PP）途径、苹果酸酶和由丙酮酸羧化酶（pycA）催化的回补反应中的通量调节发生了变化。通量比分析表明，葡萄糖主要通过糖酵解转化，这突出了尽管条件不同该菌中央碳代谢的稳定性。在所有条件下，通过丙酮酸（PYR）反应生成草酰乙酸（OAA）的通量比更高，这表明该菌中丙酮酸羧化酶（pycA）被激活，以应对指数生长期的酸胁迫。随后，在氧化和非氧化磷酸戊糖（PP）途径、苹果酸酶以及丝氨酸和C1代谢中观察到更显著的通量比差异，这表明对环境刺激的NADPH需求。这些反应可能在该菌代谢工程的优化策略中发挥重要作用。总体而言，氨基酸系统分析和通量比分析的整合提供了一个系统层面的理解，即该菌如何在各种条件下调节中央代谢。
