Guo Tingting, Zhang Li, Xin Yongping, Xu ZhenShang, He Huiying, Kong Jian
State Key Laboratory of Microbial Technology, Shandong University, Jinan, People's Republic of China.
State Key Laboratory of Microbial Technology, Shandong University, Jinan, People's Republic of China
Appl Environ Microbiol. 2017 Oct 17;83(21). doi: 10.1128/AEM.01659-17. Print 2017 Nov 1.
is an obligatory heterofermentative lactic acid bacterium that produces high levels of acetate, which improve the aerobic stability of silages against deterioration caused by yeasts and molds. However, the mechanism involved in acetate accumulation has yet to be elucidated. Here, experimental evidence indicated that aerobiosis resulted in the conversion of lactate to acetate after glucose exhaustion in ATCC 367 (GenBank accession number NC_008497). To elucidate the conversion pathway, analysis showed that lactate was first converted to pyruvate by the reverse catalytic reaction of lactate dehydrogenase (LDH); subsequently, pyruvate conversion to acetate might be mediated by pyruvate dehydrogenase (PDH) or pyruvate oxidase (POX). Transcriptional analysis indicated that the and genes of ATCC 367 were upregulated 37.92- and 18.32-fold, respectively, by oxygen and glucose exhaustion, corresponding to 5.32- and 2.35-fold increases in the respective enzyme activities. Compared with the wild-type strain, the transcription and enzymatic activity of PDH remained stable in the Δ mutant, while those of POX increased significantly in the Δ mutant. More lactate but less acetate was produced in the Δ mutant than in the wild-type and Δ mutant strains, and more HO (a product of the POX pathway) was produced in the Δ mutant. We speculated that the high levels of aerobic acetate accumulation in ATCC 367 originated mainly from the reuse of lactate to produce pyruvate, which was further converted to acetate by the predominant and secondary functions of PDH and POX, respectively. PDH and POX are two possible key enzymes involved in aerobic acetate accumulation in lactic acid bacteria (LAB). It is currently thought that POX plays the major role in aerobic growth in homofermentative LAB and some heterofermentative LAB, while the impact of PDH remains unclear. In this study, we reported that both PDH and POX worked in the aerobic conversion of lactate to acetate in ATCC 367, in dominant and secondary roles, respectively. Our findings will further develop the theory of aerobic metabolism by LAB.
是一种 obligatory 异型发酵乳酸菌，能产生高水平的乙酸盐，这提高了青贮饲料对酵母和霉菌引起的变质的有氧稳定性。然而，乙酸盐积累所涉及的机制尚未阐明。在此，实验证据表明，在 ATCC 367（GenBank 登录号 NC_008497）中，葡萄糖耗尽后，好氧状态导致乳酸转化为乙酸盐。为了阐明转化途径，分析表明乳酸首先通过乳酸脱氢酶（LDH）的逆催化反应转化为丙酮酸；随后，丙酮酸转化为乙酸盐可能由丙酮酸脱氢酶（PDH）或丙酮酸氧化酶（POX）介导。转录分析表明，ATCC 367 的 和 基因分别因氧气和葡萄糖耗尽而上调 37.92 倍和 18.32 倍，相应的酶活性分别增加 5.32 倍和 2.35 倍。与野生型菌株相比，PDH 的转录和酶活性在 Δ 突变体中保持稳定，而 POX 的转录和酶活性在 Δ 突变体中显著增加。与野生型和 Δ 突变体菌株相比，Δ 突变体产生的乳酸更多但乙酸盐更少，并且在 Δ 突变体中产生的 HO（POX 途径的产物）更多。我们推测，ATCC 367 中高水平的好氧乙酸盐积累主要源于乳酸的再利用以产生丙酮酸，丙酮酸分别通过 PDH 和 POX 的主要和次要功能进一步转化为乙酸盐。PDH 和 POX 是参与乳酸菌（LAB）好氧乙酸盐积累的两种可能的关键酶。目前认为，POX 在同型发酵乳酸菌和一些异型发酵乳酸菌的好氧生长中起主要作用，而 PDH 的影响尚不清楚。在本研究中，我们报道 PDH 和 POX 在 ATCC 367 中乳酸到乙酸盐的好氧转化中分别起主要和次要作用。我们的发现将进一步发展乳酸菌好氧代谢的理论。
