Department of Food and Bioproduct Sciences, College of Agriculture and Bioresources, University of Saskatchewan, 51 Campus Drive, Saskatoon, SK S7N 5A8, Canada.
Appl Microbiol Biotechnol. 2013 Oct;97(19):8693-703. doi: 10.1007/s00253-013-5108-2. Epub 2013 Aug 4.
Lactobacillus panis PM1 belongs to the group III heterofermentative lactobacilli and can utilize various NADH-reoxidizing routes (e.g., citrate, glycerol, and oxygen) according to environmental conditions. In this study, we investigated the ability of L. panis PM1 to produce succinate, acetate, and lactate via citrate utilization. Possible pathways, as well as regulation, for citrate metabolism were examined on the basis of the genome sequence data and metabolic profiles of L. panis PM1. The presence of citrate led to the up-regulation, at the transcriptional level, of the genes encoding for citrate lyase, malate dehydrogenase, and malic enzyme of the citrate pathways by 10- to 120-fold. The transcriptional regulator of the dha operon coding for glycerol dehydratase of L. panis PM1 repressed the expression of the citrate lyase gene (10-fold). Metabolite analyses indicated that the transcriptional enhancement by citrate stimulated succinate yield. Citrate metabolism contributed to energy production by providing a major alternate pathway for NAD(+) regeneration and allowed acetyl phosphate to yield acetate/ATP instead of ethanol/NAD(+). Additionally, a branching pathway from oxaloacetate to pyruvate increased the pool of lactate, which was then used to produce ATP during stationary phase. However, the redirection of NADH-to-citrate utilization resulted in stress caused by end-products (i.e., succinate and acetate). This stress reduced succinate production by up to 50 % but did not cause significant changes at transcriptional level. Overall, citrate utilization was beneficial for the growth of L. panis PM1 by providing a NAD(+) regeneration route and producing extra ATP.
屎肠球菌 PM1 属于 III 组异型发酵乳杆菌，可根据环境条件利用各种 NADH 再氧化途径（例如柠檬酸、甘油和氧气）。在本研究中，我们研究了屎肠球菌 PM1 通过利用柠檬酸生产琥珀酸、乙酸和乳酸的能力。根据屎肠球菌 PM1 的基因组序列数据和代谢谱，研究了柠檬酸代谢的可能途径以及调控机制。柠檬酸的存在导致柠檬酸途径中的柠檬酸裂解酶、苹果酸脱氢酶和苹果酸酶的基因在转录水平上上调了 10-120 倍。屎肠球菌 PM1 的编码甘油脱水酶的 dha 操纵子的转录调节因子抑制了柠檬酸裂解酶基因的表达（10 倍）。代谢物分析表明，柠檬酸的转录增强刺激了琥珀酸的产量。柠檬酸代谢通过提供 NAD(+)再生的主要替代途径为能量产生做出贡献，并允许乙酰磷酸产生乙酸/ATP 而不是乙醇/NAD(+)。此外，从草酰乙酸到丙酮酸的分支途径增加了乳酸池，然后在静止期用于产生 ATP。然而，NADH 到柠檬酸的利用的重定向导致终产物（即琥珀酸和乙酸）引起的应激。这种应激导致琥珀酸的产量降低了多达 50%，但在转录水平上没有引起显著变化。总的来说，柠檬酸的利用通过提供 NAD(+)再生途径和产生额外的 ATP 有利于屎肠球菌 PM1 的生长。
