Major Role of NAD-Dependent Lactate Dehydrogenases in the Production of L-Lactic Acid with High Optical Purity by the Thermophile Bacillus coagulans
Major Role of NAD-Dependent Lactate Dehydrogenases in the Production of L-Lactic Acid with High Optical Purity by the Thermophile Bacillus coagulans
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DOI：
10.1128/aem.01864-14
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发表时间：
2014-12-01
影响因子：
4.4
通讯作者：
Yu, Bo
中科院分区：
文献类型：
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作者：
Wang, Limin;Cai, Yumeng;Yu, Bo
凝结芽孢杆菌2-6是光学纯L-乳酸的优良生产者。然而，很少有人知道的高光学纯L-乳酸的合成机制，由该菌株产生。系统研究了乳酸产生的3种酶-NAD依赖的L-乳酸脱氢酶（L-nLDH;由ldhL编码）、NAD依赖的D-乳酸脱氢酶（D-nLDH;由ldhD编码）和乙醇酸氧化酶（GOX），以研究这些酶与乳酸光学纯度之间的关系。德氏乳杆菌保加利亚亚种保加利亚乳杆菌DSM 20081（D-乳酸生产者）和植物乳杆菌亚种（Lactobacillus plantarum subsp. plantarum DSM 20174（DL-乳酸生产者）作为比较菌株，除了B之外，还在该研究中进行了检查。凝结物在体内和体外的乳酸生产的关键酶的比活性，其特征在于，在发酵过程中的ldhL，ldhD，和GOX基因的转录水平也进行了分析。L-nLDH和D-nLDH在L-、D-和DL-乳酸产生菌中的催化活性不同。在B中仅检测到L-nLDH活性。在天然条件下的凝结蛋白2-6，和B中ldhL的转录水平。在所有生长阶段，凝结物2-6的表达量均远高于ldhD或GOX基因。然而，对于本研究中使用的两种乳杆菌菌株，ldhD转录水平高于ldhL。L-nLDH对丙酮酸的高催化效率以及ldhL对ldhD和ldhL对GOX基因的高转录比为B产生高光学纯度的L-乳酸提供了关键解释。凝结蛋白2-6。
Bacillus coagulans 2-6 is an excellent producer of optically pure L-lactic acid. However, little is known about the mechanism of synthesis of the highly optically pure L-lactic acid produced by this strain. Three enzymes responsible for lactic acid production-NAD-dependent L-lactate dehydrogenase (L-nLDH; encoded by ldhL), NAD-dependent D-lactate dehydrogenase (D-nLDH; encoded by ldhD), and glycolate oxidase (GOX)-were systematically investigated in order to study the relationship between these enzymes and the optical purity of lactic acid. Lactobacillus delbrueckii subsp. bulgaricus DSM 20081 (a D-lactic acid producer) and Lactobacillus plantarum subsp. plantarum DSM 20174 (a DL-lactic acid producer) were also examined in this study as comparative strains, in addition to B. coagulans. The specific activities of key enzymes for lactic acid production in the three strains were characterized in vivo and in vitro, and the levels of transcription of the ldhL, ldhD, and GOX genes during fermentation were also analyzed. The catalytic activities of L-nLDH and D-nLDH were different in L-, D-, and DL-lactic acid producers. Only L-nLDH activity was detected in B. coagulans 2-6 under native conditions, and the level of transcription of ldhL in B. coagulans 2-6 was much higher than that of ldhD or the GOX gene at all growth phases. However, for the two Lactobacillus strains used in this study, ldhD transcription levels were higher than those of ldhL. The high catalytic efficiency of L-nLDH toward pyruvate and the high transcription ratios of ldhL to ldhD and ldhL to the GOX gene provide the key explanations for the high optical purity of L-lactic acid produced by B. coagulans 2-6.